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A photochemical study of crystalline dibenzobarrelene diesters : the di-[pi]-methane photorearrangement… García Garibay, Miguel Angel 1988

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A PHOTOCHEMICAL STUDY OF CRYSTALLINE DIBENZOBARRELENE DIESTERS THE  DI -»r-METHANE PHOTOREARRANGEMENT IN THE SOLID STATE. By M i g u e l Angel G a r c i a G a r i b a y B.Sc,  U n i v e r s i d a d Michoacana, Mexico, 1982  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE  REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in THE  FACULTY' OF GRADUATE STUDIES (DEPARTMENT OF CHEMISTRY)  We a c c e p t t h i s t h e s i s as conforming to the r e q u i r e d s t a n d a r d  THE UNIVERSITY OF BRITISH COLUMBIA October 1988  © M i g u e l Angel G a r c i a Garibay, 1988  In  presenting this  degree at the  thesis  in  University of  partial  fulfilment  of  of  department  this or  thesis for by  his  or  requirements  British Columbia, I agree that the  freely available for reference and study. I further copying  the  representatives.  an advanced  Library shall make it  agree that permission for extensive  scholarly purposes may be her  for  It  is  granted  by the  understood  that  head of copying  my or  publication of this thesis for financial gain shall not be allowed without my written permission.  Department  of  r^BUlSTHJ  The University of British Columbia Vancouver, Canada  Date  DE-6 (2/88)  bee~L MM  ABSTRACT  The di-7r-methane photorearrangement first  has  been  investigated  time i n the s o l i d s t a t e . A s e r i e s o f symmetric  mixed (-CC^Ri * substrates,  for  the  (-CO2R1 = -CO2R2)  and  -CO2R2) 11,12-dibenzobarrelene d i e s t e r s , used as the model  r e a c t e d i n the s o l i d s t a t e w i t h e f f i c i e n c i e s  t h a t are  similar  to those observed i n s o l u t i o n . P h o t o l y s i s o f symmetric gave  d i e s t e r s i n s o l u t i o n and i n  a s i n g l e d i b e n z o s e m i b u l l v a l e n e photoproduct. Two R^ = R2 = i P r ) t u r n e d out  Et and crystal  modifications  (iPr)  be  dimorphic  diesters with  and  in  absolute  near q u a n t i t a t i v e  in  dispersion  the  case  analysis.  crystallographic  of  the  The  results  where o n l y one o f the  four  f o l l o w e d i n the s o l i d  state.  Mixed  diesters  t h a t formed  gave  compounds  stereochemical an  degenerate  of  correlation  Photolysis  photoproduct  and  the  solution  pathways  used  media.  to  analyze  the  ability  o f the c a r b o n y l groups, which  to  be  photoproducts  The  e n e - d i o a t e c o n f o r m a t i o n on the s o l i d s t a t e r e g i o s e l e c t i v i t y . delocalizing  X-ray  seems  solid  state  correlation  between the n a t u r e o f the e s t e r s u b s t i t u e n t and the p h o t o c h e m i c a l was  was  by X-ray anomalous  upon p h o t o l y s i s two r e g i o i s o m e r i c  information  with  extremely h i g h s t e r e o s e l e c t i v i t y  i n n e a r l y e q u a l amounts i n s o l u t i o n  structural  their  syntheses  r e g i o s e l e c t i v i t y v a r i e d from moderate to h i g h w i t h no apparent  X-ray  =  (80%, E t ) e n a n t i o m e r i c y i e l d s .  isopropyl  indicated  state  (R^ = R2  one  asymmetric  The a b s o l u t e c o n f i g u r a t i o n o f the s t a r t i n g m a t e r i a l and obtained  solid  h a v i n g the c h i r a l space group P2^2^2^.  o f the c h i r a l c r y s t a l s r e s u l t e d quantitative  to  the  results.  e f f e c t o f the The  radical  i s e x p e c t e d to depend  on the degree of c o n j u g a t i o n w i t h the c e n t r a l v i n y l bond, to  play  an  important  role  e x c e l l e n t c o r r e l a t i o n was photochemical  results.  t i g h t l y packed v i n y l  in  In  solid  d e t e r m i n i n g the s o l i d s t a t e r e s u l t s .  general,  the  diesters  containing  active  and  b u t y l / i s o p r o p y l compound were found  r e a c t i o n o c c u r r e d a t the  racemic to  sec-butyl  forms.  form  a  groups  state  A t h i r d example o f a b s o l u t e was  solid  solution  discovered  when  asymmetric  photolysis  o f the racemate  the  least  were  the  diisoproin  the  generated  Photochemi-  c a l and s p e c t r o s c o p i c r e s u l t s from the m e t h y l / s e c - b u t y l compound example o f s o l i d s o l u t i o n o f the enantiomers,  of  synthesis  o p t i c a l l y a c t i v e products with very high enantiomeric y i e l d s .  a second  An  C r y s t a l s o f the sec-  t h a t i s isomorphous w i t h the c h i r a l c r y s t a l s o f the  p y l compound.  seem  carbon.  optically  enantiomers  not  found between s o l i d s t a t e s t e r i c f a c t o r s and  C h i r a l dibenzobarrelene studied  in  does  indicated  but t h i s time  with  Lack o f d i a s t e r e o s l e c t i v i t y i n the s o l i d  state  ) a  racemic  space  group.  r e a c t i o n o f the l a t t e r compound was steric  rationalized  in  terms  of  efficient  c o n t r o l i n the s o l i d s t a t e r e a c t i o n but i n e f f i c i e n t s t e r i c  control  d u r i n g the c r y s t a l l i z a t i o n p r o c e s s . An unusual and  s o l i d s t a t e luminescence  o f the  11,12-diesters  was  noted  a n a l y z e d i n terms o f the b i r a d i c a l i n t e r m e d i a t e s p o s t u l a t e d a l o n g the  di-w-methane rearrangement pathway. F i n a l l y , photochemical  the s o l u t i o n and s o l i d  state  r e s u l t s from d i b e n z o b a r r e l e n e s b e a r i n g an e s t e r group a t the  b r i d g e h e a d p o s i t i o n are  analyzed.  -iv-  TABLE OF CONTENTS  page ABSTRACT  i i  LIST OF TABLES  .  ix  LIST OF FIGURES  xi  ACKNOWLEDGMENTS  xix  INTRODUCTION  1  The Topochemical P o s t u l a t e  2  S o l i d S t a t e Chemical R e a c t i v i t y  5  1. Number o f Components  6  2. Thermodynamic F a c t o r s  11  3. K i n e t i c Requirements  13  Photochemical Reactions i n Molecular  Crystals  . . .  20  E x c i t e d State P a r t i t i o n i n g  22  The Di-7r-Methane  26  Rearrangement  The R e g i o s e l e c t i v i t y o f the Di-7r-Methane Rearrangement  32  O b j e c t i v e s o f Present of the Thesis  34  Research and O u t l i n e  RESULTS AND DISCUSSION  41  Preparation o f Substrates  42  11,12-Dibenzobarrelene D i e s t e r s 10,11- and 9,11-Dibenzobarrelene  42 Diesters  . . . . 46  -V-  PART  I.  THE  DI-TT-METHANE  REARRANGEMENT  IN  THE SOLID STATE  49  On the True S o l i d S t a t e N a t u r e o f the Rearrangement  52  The L i m i t i n g C o n v e r s i o n on the S o l i d R e a c t i o n o f D i e s t e r Me/Me-18  State 55  P e r t u r b a t i o n s o f the E x c i t e d S t a t e Decay Channels o f C r y s t a l l i n e 18 by A c c u m u l a t i o n of Photoproduct  56 60  a) Luminescence Measurements b) C o n v e r s i o n  Dependence o f the R e l a t i v e 64  Quantum Y i e l d s o f R e a c t i o n o f 18 Mechanical  E f f e c t s and L i m i t i n g C o n v e r s i o n  . . .  67  The C r y s t a l and M o l e c u l a r S t r u c t u r e o f D i e s t e r 18 . . . PART I I . STUDIES ON SYMMETRIC DIBENZOBARRELENE  70  DIESTERS  72  Photochemistry  i n Solution  74  Photochemistry  i n the S o l i d S t a t e  75  The S o l i d S t a t e M o l e c u l a r S t r u c t u r e s o f the D i e t h y l D i e s t e r 21 The S o l i d S t a t e M o l e c u l a r S t r u c t u r e o f the D i - n - P r o p y l D i e s t e r 22 The S o l i d S t a t e M o l e c u l a r  75 79  Structure  o f the D i i s o p r o p y l D i e s t e r 23  80  Conformational  83  Polymorphism  S p e c t r a l D i f f e r e n c e s Between the Dimorphs o f D i e s t e r s E t / E t - 2 1 and i P r / i P r - 2 3 D i e t h y l D i e s t e r 21 1) S o l i d S t a t e FTIR S p e c t r a 2)  S o l i d S t a t e CPMAS C 1 3  D i i s o p r o p y l D i e s t e r 23  NMR  Spectra  85 85 89  -vi-  1) S o l i d S t a t e FTIR S p e c t r a 2) S o l i d S t a t e CPMAS  1 3  C  NMR  91 Spectra  . . . . .  D i f f e r e n c e s i n R e a c t i v i t y between Dimorphs  . . .  93 95  M o l e c u l a r and C r y s t a l C h i r a l i t y  101  A b s o l u t e Asymmetric S y n t h e s i s  103  Asymmetric S y n t h e s i s by R e a c t i o n o f D i e t h y l E s t e r 21  108  Asymmetric S y n t h e s i s by R e a c t i o n o f D i e s t e r 23  . .I l l  M e c h a n i s t i c I m p l i c a t i o n s o f the S o l i d S t a t e Asymmetric S y n t h e s i s C o r r e l a t i o n o f the A b s o l u t e S t e r e o c h e m i s t r y of the C r y s t a l l i n e D i i s o p r o p y l D i e s t e r p r o - ( - ) - 2 3 ( P 2 2 2 Form) and i t s O p t i c a l l y Pure Photoproduct ( - ) - D i b e n z o s e m i b u l l v a l e n e 57  116  S t u d i e s on the Spontaneous R e s o l u t i o n o f D i e s t e r 23  120  1  1  115  1  1) Enantiomorphism o f C h i r a l C r y s t a l s o f D i e s t e r 23 from E t h a n o l S o l u t i o n  121  2) Enantiomorphism o f C h i r a l C r y s t a l s o f D i e s t e r 23 Grown from the M e l t i n Open Containers  123  3) Enantiomorphism i n C r y s t a l s o f D i e s t e r 23 Grown from the M e l t i n a S e a l e d C o n t a i n e r . . .  124  4) Enantiomorphism i n C r y s t a l s o f D i e s t e r 23 Grown from the M e l t i n a S e a l e d C o n t a i n e r (B) . .  125  PART  III.  THE REGIOSELECTIVITY  REARRANGEMENT  IN  OF  THE  DI-TT-METHANE  T H E SOLID S T A T E  129  Compounds S t u d i e d and I d e n t i f i c a t i o n o f Photoproduct S t e r e o c h e m i s t r y  129  P h o t o l y s i s o f Mixed D i e s t e r s i n S o l u t i o n and i n the S o l i d S t a t e  140  A n a l y s i s o f the S o l u t i o n R e g i o s e l e c t i v i t y  . . . .  142  -vii-  A Primary  Steric Effect?  A Secondary S t e r i c The  142  Effect?  Regioselectivity  147  i n the S o l i d S t a t e  S t e r e o e l e c t r o n i c F a c t o r s i n the S o l i d S t a t e S o l i d S t a t e Primary S t e r i c Compression Regioselectivity  Steric  157 . . . .  158  Effects. 164  i n Chiral Crystals  of D i e s t e r i P r / i P r - 2 3  172  The  173  S o l i d S t a t e R e s u l t s a t Large  PART IV.  STUDIES ON CHIRAL MIXED  DIESTERS  176  Photochemistry Studies  i n Solution  178  i n the S o l i d S t a t e  186  C r y s t a l l i z a t i o n o f C h i r a l Compounds  186  The S o l i d S t a t e P r o p e r t i e s and Photochemistry o f D i e s t e r 42 Photochemistry o f the O p t i c a l l y Pure  195  Crystalline Material  201  Photochemistry  o f the Racemate o f Compound 42  . .  205  Asymmetric S y n t h e s i s by S o l i d S t a t e R e a c t i o n o f the Racemate o f 42 E x t e n t o f Asymmetric I n d u c t i o n i n C h i r a l  206  C r y s t a l s o f the Racemate  209  On the R e a c t i o n D i a s t e r e o s e l e c t i v i t y  211  The S o l i d S t a t e P r o p e r t i e s and o f D i e s t e r s Me/sBu-31 The S o l i d S t a t e P r o p e r t i e s and o f D i e s t e r 39  217  Concluding  Remarks  Photochemistry Photochemistry  229 229  -viii-  PART V . LUMINESCENCE STUDIES ON THE DIMETHYL D I E S T E R 18  232  General Observations  234  Observations  237  at  D i f f e r e n t Temperatures  E x c i t a t i o n Spectrum o f the R e d - E m i t t i n g Species  238  Observations What i s  the  at  D i f f e r e n t Wavelengths  241  P r e c u r s o r o f the R e d - E m i t t i n g  Species?  242  Is  243  t h e RE P r o d u c e d b y a n I m p u r i t y ?  What i s  the  RE S p e c i e s ?  The I d e n t i t y PART V I  o f S p e c i e s X and Y  248 256  STUDIES ON 9 - SUBSTITUTED  DIBENZOBARRELENES  265  Photolysis  of Diester  10-iPr/ll-Me-44  Photolysis  of Diester 9-iPr/ll-Me-45  267 279  EXPERIMENTAL  283  REFERENCES  348  - ix-  LIST OF  Table I  II  TABLES  Caption  Page  D i b e n z o b a r r e l e n e D i e s t e r s Prepared by E s t e r i f i c a t i o n o f D i a c i d 19 A n a l y t i c a l P h o t o l y s i s o f 18 the S o l i d S t a t e  Stepwise 45  i n S o l u t i o n and  in 54  III  Symmetrically Substituted Dibenzobarrelene D i e s t e r s  IV  R e l a t i v e Reaction E f f i c i e n c i e s of C r y s t a l l i n e Dibenzobarrelene Diesters  V  VI  VII  VIII  IX  X  XI  XII  XIII  XIV  XV  S o l i d S t a t e Induced O p t i c a l A c t i v i t y C r y s t a l s o f 21  in  S o l i d S t a t e Induced O p t i c a l A c t i v i t y C r y s t a l s o f 23  i n Single  Photolysis of Single C r y s t a l s of from Batch 3  23  P h o t o l y s i s of C h i r a l C r y s t a l s o f from Batch M e l t I  23  P h o t o l y s i s o f C h i r a l C r y s t a l s of from Batch M e l t I I  23  P h o t o l y s i s o f C h i r a l C r y s t a l s of from Batch M e l t I I I  23  .  73  96  109  112  122  123  124  G l c and H NMR R e s u l t s from S o l u t i o n o f Mixed D i b e n z o b a r r e l e n e D i e s t e r s 1  126 Photolysis 132  High Mass Fragmentation o f the Dibenzosemibullvalene Diesters G l c A n a l y s i s o f the Photoproducts o f Me/sBu-31, Et/sBu-39 and i P r / s B u - 4 2  139 Diesters  S e l e c t e d Fragment-Ions from Photoproducts D i e s t e r 42  179 of  The H NMR Resonances o f H(8d) and H(4b) from Products o f D i e s t e r i P r / s B u - 4 2 as a F u n c t i o n o f Four D i f f e r e n t S o l v e n t s  181  1  183  -x-  XVI  Relative  Yields  Of Photoproducts  from  Diester  iPr/sBu-42 XVII  Lattice 23,  XVIII  Parameters  (S)-(+)-42  (S)-(+)-42  XIX  Melting  XX  Solid  State  Solid  State  of XXII  XXIII  Points  the  of  Mixed  the  .  .  System  of  .  .  Compounds .  i n  .  .  .  .  .  198  Diesters 199  Crystals  Optical Racemate  Solid  Crystals  of  State  Proposed  Occupancies  Compound  of  .  and (R,S)-42  Induced of  Crystals .  Ene-Dioate  Relative  and  P2^2^2^  Stereoselectivity  Crystals  Structures  XXIV  of  and (R,S)-42  Conformation of 23,  XXI  184  of  from  Diester  42  .  .  .  200  Compound  42  .  .  .  201  A c t i v i t y by of  Diester  Stereoselectivity  Photolysis 42  208  from  Me/sBu-31 i n  Diesters  the 30  219  Isomorphous  a n d 31  Crystal  (optically  Racemic)  pure 228  Relative  Solid  Crystals  of  State  Compound  1  Stereoselectivity Et/sBu-39  from 229  -xi-  LIST OF FIGURES  Figure 1  2  Caption  Page  Examples o f Compounds D i s p l a y i n g D i f f e r e n t S o l u t i o n and S o l i d S t a t e r e a c t i v i t y The Polymorphic trans-Cinnamic  1  A c i d s and t h e i r  S o l u t i o n and S o l i d S t a t e R e a c t i v i t y  4  3  The D i m e r i z a t i o n o f B e n z y l i d e n e c y c l o p e n t a n o n e  8  4  An Example o f a S o l i d S t a t e Chemical  Reaction  i n an I n c l u s i o n Compound  10  5  Some Examples o f G a s - S o l i d R e a c t i o n s  11  6  D i f f e r e n c e s i n the R e a c t i o n C o o r d i n a t e between S o l u t i o n and S o l i d . S t a t e R e a c t i v i t y D i f f e r e n c e s i n Number o f A v a i l a b l e S t a t e s and R e a c t i o n Pathways Between F l u i d Media and S o l i d S t a t e R e p r e s e n t a t i o n o f : (a) A l l o w e d and (b) D i s a l l o w e d S o l i d S t a t e R e a c t i o n s i n the R e a c t i o n C a v i t y  7  8  9  Reaction  I n h i b i t i o n by S t e r i c  13  16 18  Compression  Control  19  10  J a b l o n s k i Diagram  23  11  The Di-7r-Methane R e a c t i o n Mechanism R e p r e s e n t e d i n 1,4-Pentadiene and A l l y l Benzene  27  12  The M u l t i p l i c i t y - D e p e n d e n t P h o t o c h e m i s t r y o f Barrelene  28  Examples o f S u b s t r a t e s t h a t Undergo R e a c t i o n s Other than the Di-?r-Methane Rearrangement from the S i n g l e t E x c i t e d S t a t e  30  Dienes t h a t Undergo Double Bond I s o m e r i z a t i o n I n s t e a d o f the Di-7r-Methane Rearrangement from The T r i p l e t E x c i t e d S t a t e  31  13  14  -xii-  15  16  17  18  19  20  Examples o f R e g i o s e l e c t i v e Di-7r-Methane Rearrangements  33  The Di-7r-Methane Rearrangement o f Diesters  35  Dibenzobarrelene  The f o u r Di-w-Methane Systems i n the Skeleton R e g i o i s o m e r i c Products Diesters  from  "Mixed"  Dibenzobarrelene 37 Dibenzobarrelene 38  Di-7r-Methane Rearrangement o f 10,11and 9,11-Dibenzobarrelene D i e s t e r s Synthesis of Dibenzobarrelene  40  D i e s t e r s by  Diels-Alder Reaction  42  21  A c i d C a t a l y z e d T r a n s e s t e r i f i c a t i o n o f D i e s t e r 18  22  P r e p a r a t i o n of 9-Anthracenecarboxylate  23  P r e p a r a t i o n o f 10,11- and Diesters  24  25  26  27  28  29  30  . . .  Derivatives  43  . . 46  9,11-Dibenzobarrelene 47  P a r t i a l E NMR o f : (A) 1 0 - I s o p r o p y l - l l - m e t h y l and (B) 9 - I s o p r o p y l - l l - m e t h y l - d i b e n z o b a r r e l e n e Diesters  48  The Di-7r-Methane Rearrangement o f the D i e s t e r 18  50  l  Dimethyl  D e r i v a t i z a t i b n o f P a r t i a l l y Reacted D i e s t e r 18 w i t h Diazomethane to Y i e l d the C h r o m a t o g r a p h i c a l l y Separable Adduct 53  51  Photochemical A c t i v a t i o n and Decay P r o c e s s e s A v a i l a b l e to C r y s t a l s o f Reactant 18  59  U n c o r r e c t e d F l u o r e s c e n c e and Phosphorescence S p e c t r a o f P o l y c r y s t a l l i n e 18 a t 77K (a) B e f o r e (b) A f t e r I r r a d i a t i o n w i t h the N i t r o g e n L a s e r  and  Consumption o f D i e s t e r 18 as a F u n c t i o n o f P h o t o l y s i s Time. V a r i a t i o n s i n the R e a c t i o n Quantum Y i e l d as a F u n c t i o n o f C o n v e r s i o n Photographs o f a S i n g l e C r y s t a l o f D i i s o p r o p y l D i e s t e r 23 (Pbca M o d i f i c a t i o n ) B e f o r e (top) and A f t e r P h o t o l y s i s (bottom)  63  66  . 69  -xiii-  31  32  Stereoview o f the M o l e c u l a r the Dimethyl D i e s t e r 18  34  71  Stereoviews o f the M o l e c u l a r S t r u c t u r e s o f the D i e t h y l D i b e n z o b a r r e l e n e D i e s t e r 21 i n (a) t h e P2 /c and (b) P 2 2 2 M o d i f i c a t i o n s . . . . . . . . .  78  Stereoview o f the M o l e c u l a r Structure o f the D i - n - p r o p y l D i e s t e r 22 (Space group PI)  79  1  33  Structure of  1  1  1  Stereoviews o f the M o l e c u l a r S t r u c t u r e s o f the D i i s o p r o p y l D i e s t e r 23 i n i t s (a) P 2 2 2 and (b) 1  1  1  Pbca M o d i f i c a t i o n s  82  35  The M o l e c u l a r  36  S o l i d S t a t e FTIR S p e c t r a o f D i e s t e r E t / E t - 2 1 in i t s P2 2 2 (top) and P 2 / c M o d i f i c a t i o n s (bottom) . 86  37  CPMAS C NMR S p e c t r a o f E t / E t - 2 1 i n i t s (a) P 2 2 2 and (b) P 2 / c M o d i f i c a t i o n s  90  S o l i d S t a t e FTIR S p e c t r a o f D i e s t e r 23 i n i t s (A) P 2 2 2 and (B) Pbca M o d i f i c a t i o n s  92  CPMAS C NMR S p e c t r a o f i P r / i P r - 2 3 i n i t s (A) Pbca and (B) P 2 2 2 M o d i f i c a t i o n s  94  S o l u t i o n and S o l i d S t a t e Photochemistry o f Azobisisobutyronitrile  98  S o l u t i o n and S o l i d S t a t e Photochemistry o f a-adamantyl-p-chloro-acetophenone  99  1  1  1  1  41  42  43  44  45  46  83  1  1  1  1 3  1  40  . . . . . . .  1  1  39  o f Lepidopterane  1 3  1  38  1  Structure  1  1  The Four R e a c t i o n Pathways o f S y m m e t r i c a l l y Substituted Dibenzobarrelene Diesters  101  S o l i d S t a t e Photochemistry o f C h i r a l C r y s t a l s o f Pure and Mixed A r y l Butadienes  107  Asymmetric S y n t h e s i s by R e a c t i o n o f Unsymmetrically S u b s t i t u t e d V i n y l D i a c r y l a t e s  . . . .  107  The Four Non-Equivalent Protons i n the Methylene Groups the D i e t h y l D i b e n z o s e m i b u l l v a l e n e Diester 5 5  110  P a r t i a l H NMR S p e c t r a (300 MHz) o f Racemic ( t o p ) and O p t i c a l l y A c t i v e (bottom) D i e s t e r 5 7 a f t e r A d d i t i o n o f 1 eq o f E u ( h f c )  114  X  3  -xiv-  47  Absolute  48  Sterodiagrams (a)  Configuration of with  Absolute  i n pro-(-)  Enatiomorph,  Environment  of  Diester  and (c)  Possible  Reaction for  the  Spontaneous  23  117  Configuration  23  Account 50  (-)-57  Diester  Dibenzosemibullvalene 49  Diester  of:  (b)  Local  Diisopropyl  (-)-57  Pathways  118 of  Diester  Observed Absolute  Resolution  of  23  that  Configuration  .  .  .  Ethyl-Allyl-Anilinium  Iodide 51  Mixed  127 Diesters  Used  Regioselectivity  53  Dibenzobarrelene  Independent  the  NMR S p e c t r a a n d 63B  of  Stereospecific  Bond  Solution  Compounds  a  of  of  63A  Diesters  and S o l i d  28  to  .  .  .  State  39  141  by Bridgehead  Primary of  the the  (R)  Steric  Effect  on  the Di-7r-Methane  Steric Carbon  Dibenzobarrelenes Interactions  Attached  to  .  .  n-Systems  The T r i p l e t  by the  (6)  Energy  System  Between  as  of a  an Function  the Mean  Planes  of of 148  Excited  State  of  Dibenzobarrelenes  1,2-Biradical Radical  145  146  Carbonyl  Two  138  143  the Resonance  Torsion Angle  Free  133  Induced  9-substituted  the  a  63A  Substituent  Variations  as 62  of  of  Relief  a,^-unsaturated  61  Impact  Stabilization  Formation at  Bulkier 60  the  Regioselectivity  Possible  Photoproduct  i n BR-2  Rearrangement 59  131  Dibenzosemibullvalene  of  The Involvement the  Diesters  134  Electron of  Center  Substituents  of  Rearrangement  Dibenzosemibullvalenes  Comparison Between  Radical  the  (bottom)  Regioselectivity  58  Di-jr-Methane  Synthesis  Fragmentation  57  of  129  of  Mixed  Study  .  from  (top)  56  the  the Di-7r-Methane  Products  54  55  i n  of  Rearrangement 52  119  Rearrangement  149 of  Dibenzobarrelenes  .  .  .  150  -XV-  63  R e g i o s e l e c t i v i t y o f D i b e n z o b a r r e l e n e Monoesters  64  E f f e c t o f the A l k y l S u b s t i t u e n t s on t h e C a r b o n y l A b s o r p t i o n Frequency o f A l k y l Benzoates  152  Gas Phase Conformation o f D i b e n z o b a r r e l e n e D i e s t e r s O b t a i n e d from M o l e c u l a r Mechanics (MMP2) . .  156  S t e r e o e l e c t r o n i c E f f e c t s o f t h e C a r b o n y l Groups on the P r e d i c t e d and Observed R e g i o s e l e c t i v i t y from the Di-w-Methane Rearrangement o f Some Dibenzobarrelene Diesters  160  Photochemical D i f f e r e n c e s between the Conjugated and Non-Conjugated Rotamers o f B e n z o y l Naphthobarrelene 73  162  Displacement o f the V i n y l - A t t a c h e d S u b s t i t u e n t D u r i n g the B e n z o - V i n y l B r i d g i n g Step on V i n y l D i s u b s t i t u t e d Dibenzobarrelenes  165  L a t t i c e Environment Around the V i n y l S u b s t i t u e n t s of the D i e s t e r s Me/iPr-30 and Me/Ph-37  166  S i m u l a t i o n o f the A r y l - V i n y l B r i d g i n g Step i n the Di-7r-Methane Rearrangement o f Dibenzobarrelenes  169  P l o t s o f the Change i n P a c k i n g P o t e n t i a l Energy d u r i n g the F i r s t Step o f the Di-7r-Methane Rearrangement o f D i b e n z o b a r r e l e n e s Me/iPr-30 and Me/Ph-37  171  65  66  67  68  69  70  71  72  73  74  75  76  . . .  Changes i n the PPE d u r i n g the F i r s t Step o f t h e Di-7r-Methane Rearrangement o f D i e s t e r i P r / i P r - 2 3 The Di-7r-Methane Rearrangement o f C h i r a l Diesters  . .  150  173  Mixed 177  Mass S p e c t r o m e t r i c Fragmentation o f the Photoproducts from S e c - b u t y l C o n t a i n i n g Dibenzobarrelene Diesters Regioselective Preparation of D i b e n z o s e m i b u l l v a l e n e s 7 5 I / 7 5 I I and 7 4 I / 7 4 I I  180  . . . .  B i n a r y Phase Diagrams o f (a) the Racemic M i x t u r e , (b) the Racemic Compound and, ( c ) S o l i d S o l u t i o n s (Mixed C r y s t a l s ) o f the Enantiomers  182  188  -xvi-  77  S o l i d S o l u t i o n with S t a t i s t i c a l Disorder  192  78  S o l i d S o l u t i o n w i t h Short Range Order  193  79  S o l i d S o l u t i o n with N o n - S t a t i s t i c a l Symmetry Order  193  80  81  82  83  84  Inverse  S o l i d S t a t e FTIR S p e c t r a o f C h i r a l P 2 2 2 C r y s t a l s o f D i e s t e r i P r / s B u - 4 2 : (a) Racemic and (b) O p t i c a l l y Active  196  C o n v e r s i o n o f the Photoproducts from ( S ) - ( + ) - 4 2 i n t o the Dimethyl D i b e n z o s e m i b u l l v a l e n e ( + ) - 5 2 . . .  203  Formation o f D i b e n z o s e m i b u l l v a l e n e s from ( S ) - ( + )-42  204  1  1  1  7 5 1 and 7 5 1 1  S t r u c t u r a l P o s s i b i l i t i e s f o r the Photoproducts from D i e s t e r (+)-sBu/iPr-42  206  ^-H NMR S p e c t r a o f Racemic (top) and O p t i c a l l y A c t i v e (bottom) D i b e n z o s e m i b u l l v a l e n e 52 a f t e r A d d i t i o n o f 1 eq o f E u ( h f c )  210  The Four Modes o f Isomorphous Replacement o f D i e s t e r 23 by D i e s t e r 42  213  Loss o f D i a s t e r e o m e r i c C o n t r o l i n the Product S t e r e o c h e m i s t r y by Means o f Occupancy o f the Same C h i r a l L a t t i c e S i t e by Two D i f f e r e n t Enantiomers . .  215  Loss o f R e g i o i s o m e r i c C o n t r o l by Means o f P o s i t i o n a l D i s o r d e r i n the C r y s t a l L a t t i c e o f (R,S)-42  216  S o l i d S t a t e FTIR S p e c t r a o f (a) Racemic and (b) O p t i c a l l y Pure D i e s t e r Me/sBu-31  218  H y p o t h e t i c a l R e a c t i o n o f D i e s t e r 31 t o Give the Two Diastereomers 64A as a R e s u l t o f a Lack o f L a t t i c e C o n t r o l on the F a c e - S e l e c t i v i t y o f the Rearrangement  220  H y p o t h e t i c a l R e a c t i o n o f One Enantiomer o f 31 a t Two E n a n t i o m e r i c C r y s t a l L a t t i c e S i t e s  222  H y p o t h e t i c a l R e a c t i o n o f Two Enantiomers a t Two E n a n t i o m e r i c C r y s t a l S i t e s  223  3  85  86  87  87A  88  89  90  -xvii-  91  Reaction Sites  92  of  94  Asymmetric  Synthesis  Diacryates  76  Uncorrected  Possible  in  of  Fluorescence Anthracene  (S)-31 of  in  224  Order  to  Geometrical  Crystals  of  of  Crystals 337  Vinyl  the  Diester 236  Spectrum  of  the  Samples  Pathways  Biphotonic  of  nm  Crystalline  Formation  Appearance  in  at  Excitation  X and  and  Reaction  Pathways  231  Emission  (X)  Equivalent  227  Irradiated  Corrected  Species  97  (R)-  at  Reaction  Coefficient  (e)  Species 96  their  Similarity  Me/Me-18 95  Enantiomers  Equivalent  Comparison between Determine  93  Two  Through  for  Red-Emitting  of  the  Mechanism  Diester  18  .  .  Red-Emitting for  the  Red-Emission  Excitation  Impurity  in  (a)  243  and  Emission  Crystals  of  (b)  of  Diester  Me/Me-18 98  99  of  Excimer  Thermal  in  of  Luminescence  of  the  New  of  102  Singlet  State  103  The  The of  105 106  their  for  Two  Radical  (a)  The  Neophyl  cyclooctadienyl 87-R  Excimer 247  Species  and  Y  (a)  249 and  Emission  (b) 250  of  Dibenzobarrelenes  Rearrangement the  as  Luminescence  a of  .  .  in  the  252  Possible 254  Di-7r-Methane  Rearrangement  73  257  Fragments  of  Rearrangement Radical  .  Crystalline  Diesters  Intermediates  The  Red  Y  Naphthobarrelene  of  and  18  Red-Emitting  Reactivity  Di-7r-Methane  Spectrum  Pairs  Anthracene  Diester  Species  Species  Dibenzobarrelene 104  of  of  Excitation  Spectra  Explanation  Sandwich  246  Formation Crystals  Decay  Appearance 101  Anthracene Emission  Hypothetical Emission  100  245  Formation Red  240  87-R  BR-1  259  of  the  Spiro-  and  (b)  Absorption 261  -xviii-  107  ( a ) C o m p a r i s o n b e t w e e n BR-2 a n d t h e B e n z y l R a d i c a l , (b) S t r u c t u r e o f the D i b e z o c y c l o h e p t a d i e n y l R a d i c a l 88, a n d ( c ) E x c i t a t i o n a n d E m i s s i o n S p e c t r a o f t h e Benzyl Radical  263  108  Photochemistry  of Dibenzobarrelene Monoesters  265  109  Photochemistry  of 9-Carbomethoxy-Dibenzobarrelenes  110  The  111  10,11- and  . . .  266  9,11-Dibenzobarrelene  D i e s t e r s 44 a n d 45  267  Photochemistry  269  o f D i e s t e r 44  112  Stern-Volmer  113  Dibenzobarrelenes That D i s p l a y S i n g l e t Reactivity  State  S t e r e o v i e w s o f the P a c k i n g Diagram and S t r u c t u r e o f D i e s t e r 44  Molecular  114  .  P l o t f o r D i e s t e r 44  115  R e a c t i o n o f D i e s t e r 45  116  S t e r e o v i e w o f the M o l e c u l a r and o f D i e s t e r 45  271 274  278 280  Packing Structures 282  -xix-  ACKNOWLEDGEMENTS  I would l i k e Scheffer  t o express my  most  sincere  thanks  to  Professor  John  f o r h i s v a l u a b l e guidance and tremendous s u p p o r t throughout the  p r o g r e s s o f t h e p r e s e n t work. He does n o t spare i n t e r e s t and go w e l l beyond  advice  that  c h e m i s t r y and I have been v e r y f o r t u n a t e t o l e a r n from such  an e n t h u s i a s t i c and knowledgeable man. Lab 346 has been a p l a c e o f wonderful ences.  I  will  and  friendly  experi-  Phani  Raj  and Graham R a t t r a y deserve s p e c i a l thanks as they p r o o f r e a d the J.  Trotter  and the  o f h i s group f o r a l l t h e i r a s s i s t a n c e and c o n t i n u o u s a d v i c e . I am  s p e c i a l l y g r a t e f u l to F r e d Wireko who d i d a l l the reported i n this Financial of  sharing  environment.  e n t i r e m a n u s c r i p t . Thanks a r e a l s o due t o P r o f e s s o r members  and  always be i n d e b t e d to the members o f the group, p a s t and  p r e s e n t , f o r k e e p i n g such a f r e s h Pokkuluri  learning  crystallographic  work  thesis.  support from the U n i v e r s i t y o f B r i t i s h Columbia  a U n i v e r s i t y Graduate F e l l o w s h i p i s a l s o g r a t e f u l l y L a s t b u t n o t l e a s t I would  like  t o say:  gracias  i n the form  acknowledged. a  Mama,  Papa, l o s  G a r c i a G a r i b a y y anexas p o r haberme dado t a n t o apoyo. Los Mendoza han s i d o un gran ejemplo que siempre a p r e c i a r e .  G r a c i a s a Bety y a I n g r i d p o r s e r  f u e n t e de c o n t i n u o amor e i n s p i r a c i o n .  i  INTRODUCTION.  The rapidly  study  developing  molecular  the  area  chemical  reactions i n crystalline  of organic  chemistry.^-  c r y s t a l s can modify the " i n t r i n s i c "  reactivity of  o f organic  solids  i sa  I t i s now r e c o g n i z e d  that  o r s o l u t i o n phase  i n a manner t h a t depends d e e p l y o n t h e s t r u c t u r a l  crystal.  Many  chemical  properties  e x a m p l e s a r e known o f r e a c t i o n s t h a t o c c u r i n a  completely  d i f f e r e n t m a n n e r when c a r r i e d o u t i n s o l u t i o n o r i n t h e s o l i d  A  s e t o f r e p r e s e n t a t i v e examples where t h e s e d i f f e r e n c e s c a n be  state.  illustrated  i s shown i n F i g u r e  1 below.  Me Dimers  Ph  Ph  Ph  _.  -  c  o  Only Product  Figure Solid  .  M  Ph  -  c  Ph Ph  o  RotiD  1. E x a m p l e s o f Compounds D i s p l a y i n g  State R e a c t i v i t y .  Ph  Ph  Ph 1  :  2  Ph  Ph  Ph  Ph  :  Different  1  Solution  and  -2-  Solid  s t a t e o r g a n i c c h e m i s t r y i s an a r e a t h a t v e r y c l o s e l y  the u n d e r s t a n d i n g of  the  t h a t o r g a n i c chemists have of the  mechanistic  most  details  a s p e c t s of o r g a n i c c h e m i s t r y and o f the n a t u r e  p r o p e r t i e s of molecular c r y s t a l s . the  structural  reflects  I t i s f o r these reasons  i m p r e s s i v e demonstrations  t h a t some  and of  o f the scope o f s o l i d s t a t e o r g a n i c  c h e m i s t r y have been d i s c o v e r e d o n l y d u r i n g the l a s t twenty f i v e y e a r s . ^ I t has been s p e c u l a t e d ^ t h a t Wohler i n 1828 scientist  to  study  an  organic  s y n t h e s i z i n g u r e a from s o l i d organic  solid  state  solid  'ammonium  state  may  have been the  chemical r e a c t i o n while  cyanate.^  Sporadic  r e a c t i v i t y can be found throughout  reports  the  c e n t u r i e s . ^ I t seems t h a t a t these times  conceptual d i f f i c u l t i e s gas  and  solid  states  immense  majority,  a  gap  took  the  responsibility  organic for  e x p e r i m e n t a l , a n a l y t i c a l and t h e o r e t i c a l a s p e c t s o f the  The T o p o c h e m i c a l  the  liquid,  between  o f s o l u t i o n and gas phase r e a c t i v i t i e s on the one  and s o l i d s t a t e r e a c t i v i t y on the o t h e r . F l u i d phase the  in  and  might have been comparable. P r a c t i c a l c o n s i d e r -  a t i o n s and s t r o n g e r t h e o r e t i c a l models, however, l e d to the u n d e r s t a n d i n g  early  the e x p e r i m e n t a l  i n studying chemical r e a c t i v i t y  of  literature  w i t h a p e r i o d of i n c r e a s e d a c t i v i t y d u r i n g the l a t e n i n e t e e n t h and twentieth  first  hand  chemists,  developing  the  field.  Postulate.^  In the e a r l y 1960s X-ray c r y s t a l l o g r a p h y had been f i r m l y e s t a b l i s h e d as  the  most  important  concepts were developed  s o l i d s t a t e a n a l y t i c a l t o o l and many s t r u c t u r a l therefrom.  The  crystalline  s t a t e had become the  preferred  medium  experience study  of  Schmidt  the  last  tion  of  a  cyclodimerization basis of  the  solid  The 1918  by  organic  chemistry,  stating  molecular  arrangement  that  relatively reacting  The  points  in  the  molecular was  pairs that  can  acids  types  this  as of  related  state  the  (1)  are in  that  one  a of  reactions  manner^  A  packing  is  given  (Figure  intermolecular  2).  The  basis  and  days  the  one  by  it and  implications  of  the  the  put  atomic  controlled  of  in  three  refined  by  the  potentially  forms him  of  to  trans i l l u s -  2) . three  fundamental  geometry  2n  firm  Schmidt  minimum o f  served  key  a  the  crystals.  (Figure  7.  on  +  early  by  crystal  in  put  2ir  Kohlschutter^  between  crystallize 6  by  are  different  since  postulate.  the  with  mid  applica-  the  the  controlled  and  a,  in  enunciated  dimerization  elegant  the  Schmidt  evolved  the  known  with  the  Gerhard  during  reactions ones,  for  that  olefins,  orientations of  time  primarily  occur  state  medium  conceived  experimental  recognized  most  known  be  crystals  and  that  accumulated  studying  molecules  photochemical  cinnamic  three  first  much  primary  topochemical  strong  behavior  the  modifications  between  study  The  a  at  concept  solids  solid  distances  towards  trans  in  that  centers.^ acids  on  Schmidt  is  fixed  these  crystal  postulate  motion.^  solid  the  the  the  probably  By  as  in  of  reactions  postulate  trate  reactions  as  photochemical  intuitive  postulate  whereas  was  crystalline  state  topochemical  he  the  the  and  that  It  techniques.  many  topochemical  cinnamic  of  general  stated  the  some  especially  of  state  idea  most  dimensional the  liquid  b r i l l i a n t  analytical  studies,  reactivity.  restudied  century,  X-ray  the  chemical  executed  1940s.^  structural  maintained  organic  Schmidt  for  different difference  manner  finding  determines  in not  in  which  Schmidt's only  the  absence  or  presence  of  r e a c t i v i t y but also theproduct  t r y . - ^ The c e n t r o s y m m e t r i c  i n t e r m o l e c u l a r arrangement i n t h e a type l e d acids ( 2 ) .  to the centrosymmetric a - t r u x i l i c a r r a n g e m e n t shown t o e x i s t £-truxinic  acids  translational double acid  axis  (3)  stereochemis-  i n t h e /9  and  finally  form  The p a r a l l e l gave  t h e 7 form,  the  translational  mirror-symmetric  c h a r a c t e r i z e d by a long  and a p o o r l y overlapped arrangement between  t h e two  b o n d s , was f o u n d t o b e u n r e a c t i v e . I n t e r e s t i n g l y , t r a n s - c i n n a m i c  i n s o l u t i o n s i m p l y undergoes t r a n s - t o - c i s  Ar  hv  isomerization.  Ar  W  SOLUTION  HOOC  COOH  HOOC  COOH  Ar  Ar hv Ar Ar  a-MODIFICATION  COOH  COOH  Ar Ar  Ar hv COOH  \  p-MODIFICATION  COOH  3  COOH  COOH  hv  COOH  NO REACTION  T-MODIFICATION COOH  F i g u r e 2. The P o l y m o r p h i c and  Solid State Reactivity.  d>4.2A  trans-Cinnamic Acids  and  their  Solution  The  r e s u l t s obtained  compounds  led  with  Schmidt  to  the  cinnamic  suggest  acids  that  and  e x i s t an u p p e r l i m i t b e y o n d w h i c h r e a c t i o n can  I n the  case of  distance  between the  modification shorter  cinnamic acids  was  two  w i t h i n 3.6  double  bonds  These r e q u i r e m e n t s are which  has  Schmidt's  proposals  State  crystalline  tion.  solid  fulfilled  have  of  a parallel f o r 2n  The  by  the  often  the  phase  early of  reports  organic  of  between some cited  4.7  B  and  distance the  occur.  7-modification, and  apparent with  solid  c o n c e p t t h a t m o l e c u l a r f r e e d o m was evolved  from s t u d i e s  being  a  be  A  5.1  and  exceptions,^  the  state  a u t h o r i t y of  a  considered  handling  and  purifica-  a prerequisite for led  s o l i d s should  phenomenon. The fact  chemical  to  the  be  unreactive.^  compounds,  intuit-  i t  most i n t e r e s t i n g a s p e c t s  that  where most m o l e c u l a r m o t i o n s a r e  the  time  i n f l u i d m e d i a and  come f r o m t h e  reactivity,  for a long  common t o many c r y s t a l l i n e  general  state reactivity  conditions  a  d i m e r i z a t i o n to  unreactive  compounds was  i n c o r r e c t concept that a l l organic  from  the  arrangement between  + 2n  a  center-to-center  Schmidt suggested t h a t a  distances  been  the  occur.^  nature.  W h i l e u n r e a c t i v i t y may far  not  required  longer  double bonds o f  more t h a n a c o n v e n i e n t r e s o r t f o r e a s y  reactivity ively  was  and  no  there  Chemical R e a c t i v i t y .  In s p i t e of  nothing  A  A.  o l e f i n arrangements. Despite  fundamental law  Solid  t o 4.1  center-to-center  non-parallel  found that  reacting olefinic  t h a n a p p r o x i m a t e l y 4.2  reacting  i t was  olefinic  f o r each r e a c t i o n type  should  the  other  reactions  disallowed.^*^  occur  is of  under  Topochemical  reactions between  tend to the  reactants,  mechanistic structures It  information of  is  the  the  t o be  through  a  intermediates can  sometimes  of  components  present  d e t e r m i n e d by  during  and,  to  the  line the  1.  solid  state  and  the  state  Number o f  3)  and  and  main  state be  r e s e a r c h work i s component. try  will  i n the  the  free  Due  to the  d e t e r m i n e the  X-ray  energy  their roles  chemical  relate  to:  r e a c t i o n medium, 2) changes  the  involved  d e t e r m i n e d by  restricted  l i m i t a t i o n to the the  While the  the  free  composition  and  i n the  crystal-  i n a d i f f e r e n t manner  in  number  allowed  in  the  s o l u b i l i t y p r o b l e m s , i t i s known t h a t  homoge-  r a r e l y c o m p o s e d o f more t h a n one whether  homomolecular. out  unimolecular  At in  other areas w i l l  the  or  component.  bimolecular,  are  p r e s e n t time most s o l i d  state  molecular  I t seems, however, t h a t  h a v e on  components  solid  reaction  reactions,  carried  of  general occurrence of  number o f c o m p o n e n t s i n a s o l u t i o n  neous c r y s t a l l i n e phases are  to  the  of  i n i s o t r o p i c s o l u t i o n media.  s e l d o m l i m i t e d by  expected  from  kinetic factors  above f a c t o r s p l a y  medium.  Most s o l i d  inferred  ordered molecular arrangement p r e s e n t  r e a c t i v i t y r e l a t e s to  only  L a r g e amounts  Components.  first  reaction  the  transition states.  rigid  state,  The  is  reaction,  the  be  similarity  products.  three general factors w i l l  thermodynamic f a c t o r s  energy of  and  structural  o b s e r v e d i n a g i v e n s y s t e m . ^ These f a c t o r s  number  the  continuous  reactants.^  known t h a t  reactivity 1)  occur  crystals  the  impact that  depend  largely  with  solid on  our  a  single  state  chemis-  ability  to  manipulate  multicomponent c r y s t a l l i n e  r e a c t i o n components can situations  may  be  o c c u r and  considered  complexes  compounds a n d  (also  chemical  Fortunately,  called  molecular  compounds)  are  the  These  advantage i n  the  solutions  and  Substitutional solid  3  additional  i n some c i r c u m s t a n c e s . 1 3 - 1 6  have sometimes been used w i t h  case of mixed molecular c r y s t a l s . ^ molecular  samples.  compounds, i n t e r m e t a l l i c most  important  cases  to  consider. Substitutional foreign  of  the  compounds c a n to the  solid  "solvent"  d i s p l a y i n the  spaces otherwise  crystal.^ solid  The  s t a t e can  s o l u b i l i t y between d i f f e r e n t r e a c t a n t s to  structural  information  bring  reacting  while  It  a l s o be  should  crystal. lattice  The of the  the  into  entire  practice.  could  also  A  be  that  r a n g e f r o m no  i s easy  large  The to  amount  obtained  recognized  solubility  that a p a r t i a l l y that  the  by  starting material w i l l of  the  lattice  as  two  at  importance  of  recognize  but  of chemical  and  a  compound  environments.  crystal  is a  extent  of  of  starting  material  reactions  are  characterized  reactants  solubility.  and  the  Topotactic  by  a  conversion  a f u n c t i o n of  reaction  i n t o product are transformations.^  remarkable  products,  which  transformations  structural allows o f f e r the  for  mixed  crystal  R e a c t i o n s where a sample p r e s e r v e s i t s c r y s t a l l i n i t y conversion  the  organic  d i s p l a y i n the  determine the  crystal  for  of  solubility  having  reacted  product w i l l  or s i n g l e c r y s t a l - t o - s i n g l e c r y s t a l  solid  reserved  solubility  topotactic  between the  incorporation  dissolved i n several different crystalline  integrity  progress.!^ the  c h a r a c t e r i z e d by  much r a r e r c a s e s o f c o n t i n u o u s s o l u b i l i t y .  difficult  and  s o l u t i o n s are  " s o l u t e " m o l e c u l e s i n t o the  molecules  all  solid  during called These  similarity continuous  possibility  of  m o n i t o r i n g the r e a c t i o n through X-ray topotactic  reactions  crystallography.  by  Jones  examples  and  Thomas^  (4)  and t h e i r  photodimers  ( F i g u r e 3 ) . The s t r u c t u r a l  e v i d e n t i n t h e same  figure.  hv 11  5  F i g u r e 3. The D i m e r i z a t i o n o f B e n z y l i d e n e c y c l o p e n t a n o n e .  (5)  similarity  b e t w e e n t h e two s y m m e t r y r e l a t e d monomers a n d t h e c e n t r o s y m m e t r i c is  of  a r e known. One t h e b e s t s t u d i e d s y s t e m s i s r e p r e -  sented by the benzylidenecyclopentanones studied  Few  dimer  Some  of  molecular  the  most  complexes , ^ " ^  forces  responsible  plexes,  and,  i i )  (also  called  state  systems  and  3  i15i16  components chemical  to  this  for  long  acid  host  which  then  for  their  classified-'-  existence  as:  guest-host  complexes)  are  under  compounds  belong  to  a  been  the  of  found  of  in  time  a  photoexcited  collapses  to  the  form  When  hydrogen ketone an  aryl  is  electron the  the  systems,  according  3  and  role,  and  the  transfer  com-  second  compounds  the  guest.  not  reactivity  A  from  radical  derivatized  the  cavihost  participate  solutes.  complexes  s o l i d  C l a t h r a t e s ^  however,  or  abstracted  category,  intramolecular  do  the  to  multicomponent  often,  photochemical 4).  s o l i d  investigation.  Very  included  (Figure  of  intermolecular  organizing  the  i) in  some  active  category.  passive,  reactivity  periods  more  with  this  complexes^  by  primarily  Included  currently  have  acid-ketone  are  component  complexes.  play  the  3  two  packing  inclusion  ties^-  interesting  in  Exceptions  of  deoxycholic  are  photolyzed  the  deoxycholic  pair  s t e r o i d ^  is  (Figure  formed 4).  -10-  Figure Inclusion  4.  An example o f  a  Solid  State  Chemical  Reaction  in  Compound.  Additional  r e a g e n t s c a n a l s o s o m e t i m e s be c o n s i d e r e d  for solid  r e a c t i o n s when t h e y a r e a l l o w e d  to d i f f u s e i n t o the  This  f o r some known g a s - s o l i d r e a c t i o n s  is  precisely  the  case  d i f f u s i o n i s , however, s e v e r e l y l i m i t e d (Br2, this  O2,  CO2,  category  NH3,  etc.)-  a r e shown i n F i g u r e  several gas-solid,^  known.  3  to  crystal  relatively  small  state  lattice.^ where  molecules  Some i n t e r e s t i n g e x a m p l e s f a l l i n g i n 5.  O t h e r h e t e r o g e n e o u s r e a c t i o n s may and  an  take  liquid-solid^  place  at  crystal  and s o l i d - s o l i d ^  surfaces,  reactions are  2.  Thermodynamic  Factors.  I t has been r e c e n t l y argued by reactions, in and  i n general,  f l u i d media. final  Kearsley^  that  solid  a r e n o t as t h e r m o d y n a m i c a l l y v i a b l e as  Kearsley  states  S.K.  suggested  of a solid  that  the enthalpies  of  the  state  reactions initial  s t a t e r e a c t i o n a r e r e s p e c t i v e l y l o w e r and  -12-  higher 6).  with  respect to values observed  The l o w e r  energy  be  understood  by  the molecules  organic  i n the i n i t i a l  as a r i s i n g  from  in fluid  s o l u t i o n media  state of solid  the a d d i t i o n a l  i n the c r y s t a l l i z a t i o n  compounds t e n d t o c r y s t a l l i z e  state reactions  stabilization  process. *^  It  3  energy  is  i n t h e i r minimum e n e r g y  the energy  the higher enthalpy o f the s o l i d  r e q u i r e d by the product molecules  environment  of  the s t a r t i n g m a t e r i a l . ^  formation  of  a  to play a very  product  conformathe  s t a t e r e a c t i o n s comes  from  to adjust  important  molecule  in  into  role.  the  First  additional  energy  d i f f e r e n c e between required  to  energy  role the  reactant  T h i s energy  arising  i s undoubtedly mechanical  the  final  and  l o c a t e the product  starting material. steric  to  space  a source  t h a t was  originally  i n determining the i n t e g r i t y 3 3  The l a r g e r  the  more  can  be  stress.  3 3  be t h e s o u r c e the s t r u c t u r a l  energy  It  is  be  with  the  i n t e r a c t i o n s and known  s t r e s s may p l a y a v e r y  of the l a t t i c e  would  reserved f o r the  identified  from u n f a v o r a b l e p r o d u c t - l a t t i c e of internal  rigid  a l l , the  i n the space o t h e r w i s e  relaxation that follows this  reaction.  state.  product  increase  the  of  o c c u p i e d b y a n d t a i l o r made f o r t h e s t a r t i n g m a t e r i a l w i l l of  that  P e r t u r b a t i o n s t o and from the  3  medium a r e e x p e c t e d  gained  In  3  state,  can  known  t i o n s ^ - and w i t h t h e most f a v o r a b l e i n t e r m o l e c u l a r arrangement. final  (Figure  a t the l a t e r  that  the  important stages  of  -13-  Figure Solid  6. D i f f e r e n c e  i n the Reaction  Coordinate  Between S o l u t i o n and  S t a t e R e a c t i v i t y (From R e f e r e n c e 2 9 ) .  3. K i n e t i c R e q u i r e m e n t s .  The  kinetic  requirements  n e c e s s i t y f o r part of the  for  reactants  a  reaction to  acquire  to the  occur r e f e r to the free  energy  of  a c t i v a t i o n r e q u i r e d t o overcome t h e e n e r g e t i c b a r r i e r s t h a t s e p a r a t e  the  starting materials  The  and t h e p r o d u c t s a l o n g  the r e a c t i o n c o o r d i n a t e . ^  -14-  kinetic mined  barriers by  defined able  the  by  the  that  of.solution high  enthalpic  transition  the  and  enthalpy  gas  phase  and  low  reactions  entropic  state,  or  of  transition  the  activated  are  mainly  contents  complex.  state,  as  of  It  deter-  the  species  seems  reason-  shown  in  Figure  6,  This  is  on should  also  expected the  be  higher  because  motions  the  required  to  environment  activated  complex  it  not  media,  that  concerns entropy The cally  to  reactants  equilibrated  large  tives is  the  energy  to  the  have  of  of  the  that  the  k  is  states  the that  Boltzmann describe  same  with  =  constant  k  time  more  the  structure  difference  between  state  versus  The  entropy  state  exist  a  7)  defined  (and  entropy the  given  to  which the  two  reactivity,  number by  of  their  is  the  content of  dynamimolecular  states,  degenerate)  fraction  the  r e a c t a n t s . ^  vibrational  different  is  large  the  of  activation  the  in  solvent,  their  and  solution of  resist  than  A c r i t i c a l  and  entropy  state  w i l l  space  the  n^  crystals  restricted  Figure  makes  state  the  in  states.  a  media  S  where  the  solid  (n^,  fluid  molecular  transition  fluid  the  the  transition  energetically  the  of  activation.  reactants of  to.  favor  interactions  energy  E ^ we  the  in  accommodated  states  number  given  be  between in  the At  belong  entropy  difference  conformations, The  should  than  environment reach  sometimes  the  solid  would.  ideally  may  the  rigid  solution  does  in  very the  etc.  alterna-  large. system  If with  by:  ZPilnPi  and  system.  the  summation  is  carried  over  a l l  -15-  Since states,  the  complex  only  properties, the  two  states  a  small.  few  well  defined  number  for  large  possessing complexes  n^  reached  Due  to  In  the  already possess  few  starting and  sometimes that as  solid  state, very  vibrational  one  (n^)  for  a  w i l l  react,  n^  reactions  other  We c a n  reactant given  in  for can  many  n^  hand, The  the  enthalpy  reacting  while this  state. of  in  by  The  can  respectively.  The  7,  7)  7)  are  reactants  Figure  n^,  activated  many in  the  probability collisions  alternative  molecules  modes  solid  in  two  there  the  to  Figure  (Figure  simultaneously  illustrate  the  enough  put  only  states,  in  The  and  are  available  non-productive  schematically  rotational  allowed.  (two  n^  a  reaction  there  B,  freedom, may  to  similar  and  be  that  (n^=n2=n3=etc.).  entropy.  not  state  the  chemical  occur.  states  that  low  normally state  very  indicated  on  to  has  conformational  different  states  vibrational  productive  several  B,  a  be  a  A and of  occur  reactant  B respectively  material  modes  of  of  A and  reaction  ratio  number  activated  instance,  only  Suppose  reactions  reactions  for  A and  with  number for  vibrational  result  reactions,  for  the  or  can  the  n^g  required  reaction,  with  the  requirements  and  configuration  vibrations,  to  the  transition  the  for  of  complexes,  the  to  Not  occurrence  activated solution  while  states.  complex.  defined  available  conformations,  activated  fluid  highly  reactions,  an  translational  collisional  organic  conformational  different  through  the  Many  (n*)  the  In  and  A  states  determine  compared  the  be  for  two  through  may  of  substrate.  very  of  however,  occur  different  very  properties  given  is  of  reactions  be  larger  and  organic  number  w i l l  through much  most  or  reactions  occur.  Both  would  occur.  molecules  exist  the  crystal  w i l l  translation  w i l l  representing  only  molecules  activation,  i f  in  there  the is  a  -16-  large the  resemblance between t h e s t r u c t u r e a c t i v a t e d complex. I n F i g u r e  occur only  o f the s t a r t i n g material  7, a r e a c t i o n i n t h e s o l i d  _ n  REACTION B  A  A  REACTION B  m  ™~  n «  vt  A  • *  n  ^wJl5^r ETC  F L U I D MEDIA  7. D i f f e r e n c e s  SOLID STATE  i n Number o f  Pathways Between F l u i d Media and S o l i d  the molecules p a r t i c i p a t i n g  w i t h i n the proper distance  topochemical  • •  •  i  '*  not  would  REACTION A  V  If  state  t h r o u g h n^g b u t n o t t h r o u g h n*^.  REACTION A  Figure  and o f  postulate,  and  with  States  and  Reaction  State.  i na given orientation  the energetic  t o g e t h e r would have t o be p a i d  Available  solid as  state  suggested  expense o f b r i n g i n g the destruction  reaction are  of  by the  the reactants the  crystal  -17-  lattice  itself.  This  can  activation  energy  crystal  Kcal/mol)  same  can  (42  compound  as  operate  after In  reactions  than  the  averaged  time  hand,  throughout every  may  perhaps the  one  the  topochemical  M.  Cohen  for  for  The  exert of  more  are  a l l  anthracene  energy  of  the  Kcal/mol). ^ 3  topochemically  favorable  of  of  the  many  step)  the  In  is  solid  same and  has  are  much  state,  specific that  on  the  position effects  the  reaction  time  isotropic  average  been  longer The  therefore  the  alternative  intermediates  solvent.  effect  that  the  reactivity  different  effects  estimated  state  reactions  of  the  (-22  solid  lifetimes  anisotropic  important  in  crystal  pathways  recognized  is  after  postulate.  described  the  dynamic  alternative  intuitive  concept  of  defined  Cohen  "the  w i l l  a  nearly  dynamics  energy  elementary  exert  between  which  in  in  packing  and  directions.  keep  selecting  by  one  solution  and  the  most  the  liquid  the  that  anthracene  reorganization  in  realize  sublimation  state  specific on  as  found  than  most  reaction  direction.  lattice  in  surroundings  the  its  we  of  large  differentiate  identical  the  from  liquid  taken  environment  as  reagents  the  i f  diffusion  twice  that  occur  essentially  other  is  the  appreciated  the  estimated  factors  (many  and  for  Kinetic  orientation.  be  is  directly  the  atomic  movements  the  cavity  wall,  w i l l  be  crystal  and  only  reaction  "Reaction  space  in  participate constituting  which  however,  the  w i l l  resisted those  tend  by  effect  the  the in  to  pathways  crystal  reaction  closely  with  packed a  by  Cohen  w i l l  lattice  the  reaction  occupied  cause  distorted.  involving  crystal  The  reaction."  become  processes  the  C a v i t y . " ^  the  the  of  Any  general cavity  the  as  molecules  suggested pressure such  in  a  environment  minimum c o n t a c t  that on  change, of w i l l  the be  -18-  allowed  (Figure  Figure State  8.  8).  Representation  Reactions  Scheffer,  in  intermolecular  reactivity The  term  situation  and  centers. found  in  to  cannot For  be  dimerization  be  much "steric was  unreactive spite  effects  same  way  compression  specifically  the  a  (b)  Disallowed  from  identified that  of  the  was  to  Solid  arrangement  photochemical topochemically  2ir  solid  reaction  cavity  of  +  to  where  shown  describe an  the in  2n  favorable  quantitathe  used  cases  derivative  and  modify  Cohen's  control"  applied  naphthalene  towards of  have  3  anticipated  instance,  in  co-workers ^  the  and  Cavity.  specific  state  reactivity  Allowed  and  studied  this  Reaction  (a)  Trotter  tively  concept.  the  of:  unusual reactive  Figure  9  solid  state  distance  was  and  -19-  orientation  between  proposed  that  contacts,  between  and  from  those  the  the lack  the  other  double of  bonds  of  reactivity  methyl  neighboring  originated  substituents  molecules  in  the  of  lattice  >  the as  molecules.  from two  two  It  was  specific  reacting  shown  .  in  short  molecules  Figure  9.  RO REACTION  ( E - CO.CH,)  Figure  The tion  of  9.  role  Reaction  of  reaction  Gavezzotti. ^ 3  Inhibition  kinetic pathways  This  factors in  author  the  by  Steric  in  determining  solid  suggests  Compression  state  has  that  the  the  Control.  dynamics  also free  been  and  selec-  recognized  volume  around  by the  -20-  reactive vity no  centers  of a  means  the  solid  is  what  state  departure  a  attribute  determines  reaction.  from  Cohen's  of  being  a  and  perhaps  the  absence,  presence  Although  the  reaction  cavity  more  easily  free  and  volume  concept  concept,  defined  and  selectiis  by  it  possesses  readily  measurable  quantity. A of  different  solid  After  state  studying  through  the  molecules,  that  one  of  and  by  its  sometimes influence  the  Its the  new  of  potential the  a l .  state radical  proposed  the  anisotropic  McBride to  is  reactions  energy  surfaces,  or  the  from  i n Molecular  (thermal)  on  hand,  to  by  proceed  extrusion  not  under  between  the  be  the  deter-  stress so  the  stressful  reaction  this Kbar,  to  that  very  therefore  of  factors  apply  recognized  will  10  co-workers.  known  may  occur  to  that  cavity may  be  a  strong  having  their  surprising.  are  characterized  coordinates,  electronic at  and  topochemical  that  1  understanding  Crystals.  reaction  ground  other  out  hardly  state  singlet  may  generated  points  reactivity  the  McBride  behavior  pressures  McBride  structure  intermediate  stress  the  intermediates  that  reactant  chemical  by  to  reactions  intermediates.  subsequent  equivalent  (usually)  reactions,  et  approach  proposed  solid  reactive  chemical  been  reactive  the  Photochemical Reactions  Ground  of  from  contents.  on  has  of  infer  behavior  conditions.  number  McBride  may  formation  mined  a  formation  small  further  reactivity  complementary  least  states. one  of  by  continuous In the  and  along  photochemical species  involved  exists  in  an  necessarily  excited  the  excited  are  normally  visible  (VIS)  light,  be  in  found  electron  the  use  beams,  chemiluminescence 3  other of  and  state  generated  and  the  species  by  reaction  in  can  energy  also  of  coordinate  be  thermal  used.38  is  bioluminescence),  photochemical  by  (UV)  Alternatives  (gamma  excitation by  in  ultraviolet  radiation  sonoluminescence),  and  involved  absorption  methods  high  etc.),  triboluminescence  f e r .  state  discontinuous.  Although reactions  electronic  rays,  shock  chemical finally,  has  a  by  can  X-rays,  waves  methods  and  and  (as  in  (as  energy  in  trans-  8  It  is  known  generation simple  and  of  traced excited  considering results,  the  area  literature avoidance understand detailed  are  state  seem  of  known  this  when  one  8  '  3  ^  molecular  to  be  an  require  in  ordered a  model  packed  3  8  " ^  topic  measurements  gas.  This  difficulties in  a  a  system  excited  origin  of can  that  explained  a by  experimental  more  intricate  components.^ is  indeed  superficial seems  relatively  reason  other  involves  crystals A  this  Many  the  especially  their  for  on  lowest  satisfactorily  that  phenomena.  the  is  molecular  molecular  c h e m i s t r y .  considers  be  their  the  delocalized,  to  effect  crystals,  seem  as  to  Although  phenomena  reactivity  spectroscopic  3  profound  compared  in  interesting  chemical  as  s t a t e s . I t  closely  physical  species  molecular  to  the  state  b e h a v i o r .  compounds  spectroscopy  of of  phase  to  between  Electronic f e r t i l e  gas  excited  crystals  however,  interaction  crystalline  of  aromatics,  be of  and  organic  polycyclic always  the  fate  solution  states  number  that  to  review  indicate  situation involved with  a  an  in  a is  extremely of  the  systematic easy  to  carrying  out  changing  chemical  composition. solid  state  reach  and  can  be  The  complicated  spectroscopists,  to  some  expected  relationship  extent  that  w i l l  in  Excited  Partitioning.  are  a  result  not  in  of  UV  with  photon,  the  same  J a b l o n s k i ^  diagram hv.  decay  promptly  by  or  decay that  (ISC)  the  decay  and  S^-+S ) , 0  can  and  surroundings. change  the  to  as  lower  excited  Intersystem  their  in  to  a  this  is  the  lowest  take  place.  or  (R)].  states  the  and  is  the  It  symbiotic  is the  In  and  by  therefore,  absorption  electronic In  by  the  state  (S^)  of  may  S^  event  states from occur  as  fluorescence  (IC),  intersystem  internal  conversion  m u l t i p l i c i t y in  the arrow  excited  [such  of  state  excited  same  lowest  are,  species  higher  the  lost  state  and  Depopulation  reactions  crossing  and  indicated  conversion  energy  of  chemist.  (singlet).  radiative  of  by  out  photophysical  higher  state  into  state  the  excitation  S2  as  be  organic  excited  the  internal  multiplicity  of  studied  c r y s t a l s . ^  ground  classified  [such  study  surroundings  10  often  beneficial  content,  Figure  sec)  be  a  i n i t i a l  the  in  chemical  occurs  and  as  molecules  3  may  transferred  processes  non-radiative  mode  states  Most  hand,  molecular  their  is  shown  (-lO'^  other  crossing  its  an  processes  (F)],  electron  interactions  experimental  combined  After  3  state  come  energy  with  multiplicity  with  a l l  higher  unstable.^  an  marked  which  their  the  to  reactive  equilibrium  thermodynamically a  of  the  other  by  years  from  behavior  As  the  ignored  photochemical  State  on  the  arise  excited  the  form  where  singlet  of  the  transform  (S -+S^ n  heat  to  excited into  a  t r i p l e t  excited  ground  state  forbidden, Finally, state  (S]_-»T ) (T^-»S ). occur  encounters  molecular decay  the  are  populated.  designated  as  lowest  virtue  reaction  as  It  available The  triplet  these  of  potential  reorganization.  processes  becomes  by  chemical  the  Although  0  they a  or  n  we  decays  processes  spin-orbit know,  is  hypersurface  should  also  radiative  the decay  triplet of  the  are  event  energy  to  the  excited triplet  spin  mechanisms.  where  that  pointed  singlet  formally  coupling  the  be  into  an  excited  leads  out  that  state  state,  to  a  similar once  it  however,  is  phosphorescence.  SINGLETS LEGEND Absorption IC Internal  TRIPLETS  Decay  ISC Fluorescence  Intersystem ISC Singlet Reaction  /  Crossing  IC •« /  P  hv Triplet Reaction  Figure  1 0 .  Jablonski  Diagram.  Phosphorescence  -24-  Photochemical enough with  to  any  of  one  10),  on  the  state.  of  with the  there  these  depends and  compete  each  (Figure  reactions  an  rates  excited  intrinsic  a l l  other  relationship  decay  is  Turro^ state  3  kinetic in  terms  reactions,  of  constant  which  is  given  1  the  (unimolecular)  reacting  lifetime  long  (in  sec"l)  of  the  excited  the  enough  should  excited molecule  reaction lifetime  species  under of  decay  the  be  state w i l l  chemical  excited  so  can  larger  lifetime, react  excited r  =  1  the 1/r  on  (given /  The  of  this  diagram  efficiency  to  of  reactions,  particular  available  large  Associated  3  Jablonski  (kt).  process  the  excited  yield:  Ski).  reaction  Arrhenius  A exp  depends  state  the  expression,  the  reach  than  rate  quantum  reaction  consideration,  constants,  =  (the it  in  photochemical  by  constant  Skt  of  rate  a  rate  processes.^  constant  the  feasibility the  shown  a  including unimolecular  the  /  have  decay  processes  kt  kpCsec' )  A  (t) rate  called  -  they  state  between  *  The  i f  processes,  relationship  of  occur  pathways  (unimolecular) the  This  other  decay  is  will  also  the  a  rate  in  k^  ground  transition decay  (also  in  sec"^-).  the  observed  i f  case)  possesses  a  state.  Obviously,  k^  this  of  It  for  equation:  rate  by  useful  by  a  state  the  analyzed  (-E /RT)  with  on  was  may b e  given  by  Overall,  activation  energy  probability  factor  the  of  inverse  should  be  the  the  noted  A,  whether  an  (Ea)  of  the  and  on  the  sum  that  inverse  a  of  a l l  reaction  having  zero  activation  possesses  a  inverse  the  of  probability  the  case  depend  on  the  of  a  w i l l  factor,  lifetime,  In  given  energy  1  /  T,  triplet  quantum  A of  yield  quantum  and  on  accordance  the with  $  (in  sec"^),  the  excited  for  a l l  which  i f is  the  reaction  smaller  than  the  state.  reaction  the  intersystem  3  yield  of  triplet  fraction their  =  =  of  molecules  i s c  k  s  /  fraction  of  reaching  the  2  /  c  product  respective  (  k^  quantum  crossing,  yield  $ i  s  c  ,  w i l l  which  is  The  final  species  product  originally  react  known  state,  energy  high  alternatives.^-* reaction  gives  polymerization), of  lowering  the  of  as  While  <  x  molecules  K  3  /  2  fraction  triplet  a  state  photochemical  the  from  triplet  k  in  t>  of  triplet  molecules  species  which  involvement  cases  which  starting  in  the  reaction  material sometimes  of  may  that  the  primary  are  higher  species not  to  often  several  always state. be  than  reverts  one  back These  differentiate  a  in  (free to  ground decay  a  chain  radical  the  ground  quantum from  the This  thermal  photoproduct  uncommon.^  d i f f i c u l t  not  excited  may  possess  yields  this  is  corresponding  primary photoproduct,  quantum  are  the  on  constant:  >  overall  processes  from  depend  react.  formed  intermediate,  $ 3 , w i l l  formation,  that  rate  k  Sk  state  state  at  by:  the  $isc  occur  state  $isc  and  not  yield a  low  primary  quantum  reaction  that  product  /  primary  yield.  takes  moles  A better  this  of  into  primary  photoproduct  that  in  which  photoproduct  are  this  respect  reaction  goes  species  products.  The  It  f a l l  w i l l  be  into  the  seen  model  absorption two  of  light  involved  conjugated  systems  carbon.  of  are  shown  into  studied the  the in  which simplest  Figure  11  final  Zk  )  in  (  P  is the  of  P  (moles  the  of  fraction  of  final of  the  )  formed context  identified:  most  quantum y i e l d  product.  formation  in  most  products in  term  indicating  intermediate  Compounds p o s s e s s i n g  Tr-bonds  Two  of  a  the  a)  of  the  of the  two  can  as  the  this  thesis.  outcome  or  of  In the  more  different  to  different  lead  examples  primary  studied  in  this  category.  The  one  /  n  be  that  Rearrangement.  reaction  x  the  single  f i r s t  r  can  on  Di-w-Methane  r e a c t i o n s . ^  (7)  a  k  the  interest  cases  directly b)  (  to  for  includes  intermediate  special  or  rearrangement,  The  of  on  "  reactive  general  depends  reactive  thesis  two  a  account  photoproduct)  *rxn  Cases  expression  the are  this  thesis  general a  the  di-7r-methane  and b e s t . s t u d i e d  photochemical  1,4-diene  containing  rearrangement linked  models, along  to  a  a  unit  the  are  converted  vinylcyclopropane can  common  1,4-pentadiene  with  is  commonly  be  part  of  saturated, (6) a n d accepted  moiety.  isolated or  ally1  by  or  methane, benzene  mechanism.^  n  l^'r^ 6  —  r r ^ —  r r ^  £n — O ^ — girt  On 7  Figure  11.  1,4-Pentadiene  The  above  more  than  large  number  as  transition  and  mechanism,  of  whether  state.  f i r s t  for  °  proposed  predicting However,  regarding it  Reaction  Mechanism  Represented  in  Benzene.  examples.  remains to  Di-7r-Methane  A l l y l  adequate  controversy formed,  The  is  a  the true  by  Zimmerman  in  and  rationalizing  it  should  nature  of  reaction  the  be f i r s t  1967,^ the  has  results  pointed  or  of  out  biradical  intermediate  been a  that  species  merely  a  -28-  CO  NOT  Figure  Like ment  is  have  (8)  been  other  found  cyclic  The  to  an  is  that  alternatives  states  structural a  given  each  of  is  the  type  example  of  the  electrocyclic  of  reaction  be  analyzed  by  understood in  terms  reactions.  of  The  to the  second of  the  structure  and from  of  the  when  how  structure  constants  6  state,  (Figure  photochemistry  readily  rate  8.  Barrelene  pathways.  observed  as  excited  category  reactions-^  its  such  manifold.  reactive  be  Barrelene  dienes  singlet  t r i p l e t  several  determined  can  available  their  their  of  di-7r-methane rearrange-  Acyclic  from  may h a v e  include  largely  is  from  the  m u l t i p l i c i t y dependence  they  The  dependence  compound  react  the  p r o c e s s . ^  mainly  interesting  for  i s o m e r i z a t i o n s . ^ t r i p l e t  photoreactions,  react  compounds  reason  1,4-dienes  important  olefin  multiplicity-dependent  represents  1 2 ) . ^ of  The M u l t i p l i c i t y - D e p e n d e n t P h o t o c h e m i s t r y  many a  whereas  12.  ISOLATED  the  for  The  most  cis-trans singlet diene.  and This  performance is the  suited  of for  competing  -29-  chemical  processes  order  in  as  the  each  following  excited  state  relationship:  state:  ^ E C R  >  ^ D P M  >  Triplet  state:  ^kpR  >  ^knpft  >  Where:  ECR =  electrocyclic  DPM =  di-w-methane  =  According reactions  to  should  rearrangement dienes  rotor  the  the  be  in  arranged  in  decreasing  a  ^"^FR "^k^^  rearrangement. cis-trans  isomerization.  relationship as  excited  conjugation  reactions  be  reactions.  suspected  singlet  extended  The  or  rate  always  in  with  arrangements.  free  can  ^  Singlet  FR  for  for  Figure  shown  above  competitors state.  or 13  rigid are  This and  of is  electrocyclic  the  sometimes  p a r a l l e l  included  di-jr-methane  in  the  double  this  case bond  category.  -30-  NOT  Figure the  13.  ISOLATED  Examples  Di-w-Methane  of  Substrates  Rearrangement  from  that  the  undergo  Singlet  Reactions  Excited  Other  State.  than  of  In  the  triplet  an  olefinic  di-7r-methane  double  for  acyclic  exocyclic  double  bond.  state  bond,  rearrangement.  possible  14  excited  one  finds  the  or  free  rotor  effect,  The  free  rotor  olefins  such  as  Examples  from  this  cis-trans to  effect, 6 or  in  category  be  isomerization faster  than  however,  cyclic are  is  dienes  shown  the only  with  in  an  Figure  below.  NO R E A C T I O N  (Ref.  (Ref.  Figure the  14.  Di-w-Methane  Dienes  that  Undergo  Rearrangement  from  Double the  Bond  Triplet  53)  Isomerization Excited  54)  State.  Instead  of  -32-  The  Regioselectivity  The the  f i r s t  event  formation  possible C(5)  of  products  bear  of  in  the  a  cyclopropyl  can  be  different  irradiated  in  give  This  10.  formation  of  formed  it  result  phenyl  cyclopropyl  the  biradical  shown  of  in  Figure  aryl-vinyl  bonded  15.  whereas bond.  to  rearrange  rationalized stabilized  dicarbinyl  in  can  be  case  of  compound  Final  examples  become  general  part  of  electron-donating  the  12  cyclopropyl  substituents  appear  Two  at  and  C(l)  to  (Figure  of  the  preferential  10b'  Other  is  observation  species.  regioselectively  11  come  is  was  terms  10b.  11  15)  recognized  intermediate. the  9  1,3-biradical species  Figure  centers  compound  product  illustrate to  When  in  biradical  radical  gives  14  tend  the  found  the  presented  dicarbinyl  that  bonded  groups  In  Rearrangement.  mechanism  when  stability  species  aryl-aryl which  was  was  intermediate effect  reaction  substituents.  solution,  the  Di-»r-Methane  the  from  examples  readily the  that  ring  in  on  the  where  are  formation  preferred from  the  also of  over  compounds  13  an an and  electron-acceptor the  final  olefinic  product, double  -33-  Figure  15.  Examples  of  Regioselective  Di-w-methane  Rearrangements.  -34-  Objectives  The  of  f i r s t  v i a b i l i t y state. to  Present  the  objective  and  With  of  the  generality  of  this  purpose  following  solids  in  tures  which  order  to  have in  temperatures  possible  liquid  study  a  lished, be  of  and,  A in  the  of  of  system  the  E.  shown,  much  lenes,  shown  as  products  to  mechanism.^  by  The  the  can  be  basic  from  which the  a  data  according  X-ray  strucstate  conveniently  high  and  reaction  in  should  be  study  bank  media  solid  crystalline  analogs  substrates  solution  the  solid  for  related  be  the  melting  selected  closely  of  have  crystal  in  selected  analysis  should  a l l  the 15  Me  (18),  solution  20  years  that  compound  point  (mp  =  above  in  can  under to  order  be  to  estab-  study  should  facilitate  and  18  is  the  dibenzosemibullvalene understood  by  steps  a  16). few  ago.**-*  160-1°C).52  undergo  attributes  (Figure  R =  reaction  was  their  of  system  can  rearrangement  the  the  results.  possess  Ciganek,  establish  obtaining  the  of  to  should  avoid  in  state  diester  in  melting  with  products  examples  was  substrates  of  compounds  series  derivative,  earlier,  high  a  to  Thesis.  compound  the  photochemistry  presumed  relatively  the  solid  Ciganek  model  crystals  understood  the  dimethyl by  these  the  dibenzobarrelene  studied  give  (c)  into  well  interpretation  a  facilitate  order  the  research  probability  in  of  di-w-methane  (a)  the  similar  (d)  relatively  the  (b)  phases,  transform number  the  Outline  present  mind  turn  results,  melting  to  in  and  guidelines:  may  photochemical  easy  Research  a  The  identified  photochemistry  other Diels  derivatives  was  and  had  crystalline  Substituted  Alder solid  with  a  dibenzobarre-  di-w-methane  rearrangement  to  skeleton  The  of  application shown  was  in  of  16.  formation  Zimmerman's  Figure  16  biradical  follow  the  photochemical  activation  rearrangement aromatic step  carbon  by  benzene  completed the Part the  by  ring  of  this  the  population  bond  a  C(9)-C(9a)  to  give  a  formation the  thesis  is  related  compound  and  peculiarities  Diesters.  between This and  the  excited  a  vinyl  species  reacts  rearomatizing BR-2.  two  The  radical  the was of  solid  the  state. and in  the  a a  The nearby second  previously  rearrangement centers  in  BR-2  is to  16.  state  studied  in  solid  COOR  photochemistry  of  detail  to  state  in  order  photoreaction.  COOR  BR-1  COOR  BR-2  The  to  This  ROOC  triplet  dibenzosemibullvalene  15  16.  bond  18.  ROOC  Figure  BR-1.  between  in  feasibility  the  1,3-biradical  ring  diester  of  formation  biradical  the  cyclopropyl I  by  give  bond  dimethyl  verify  to  cleaving  disturbed  form  starts  and  Di-w-methane  16  Rearrangement  of  Dibenzobarrelene  -36-  It  should  be  distinctively  noted  different  Associated  with  different  reaction  each  dibenzobarrelene different two  bridging (II),  step,  pathways  Figure  17  can  be  Since  the  most  in  this  thesis  the  crystal  labeled  is  the on  mined  and  analyzed.  in  rearrangement  The of  engages on  to A - I ,  which  of  the  four  and  methodological  product  different  f i r s t  reaction  as  15  diesters  Figure  analyzed  valene  enantiomer,  identical under on  recognized  amounts  conditions  the  on  the  w i l l  symmetric  be  A-I  pathways  two  there In  are  pathways  while  where  rearrangement.  rearrangement studies  of  that  17  as  and  enantiomeric is  Part  a  16.  A-II  for  or four  shown  the  should we  be  in  When  the  four  this  class  B-II  disymmetric  of  the  thesis  discussed  in  more  detail  identify  give  of  chiral  reaction  compounds,  dibenzosemibull-  be  the  other.  expected  influence  this in  of  symmetrically  give  can  used  deter-  can  to  one  be  effect  able  products  derivatives  to  are  II  dibenzobarrelene  tool  that  give  and  resolved  (I)  the  is  16),  B-I  the  benzo-vinyl  systems  relationship  (Figure  of  carbons,  approach,  pathways  stereochemical  four  B-II.  analysis  pathways be  di-w-methane  the  The  analysis  conceptual  such  can  this  and  photoproducts  i t  aromatic  on  which  i n i t i a l  B-I  such  in  to  on  17.  formally  substitution  A-II,  dibenzosemibullvalene indicated  the  the  According  dibenzobarrelene  diesters,  in  the  four  Figure a  depending  be  on  is  recognized  can  so-called the  there  photoproducts.  reaction.  important  systems  has  in  different  C(B),  as:  highlighted  give  available  lattice  substituted  the  as  skeleton  depending  may  or  systems  1,4-diene  depending  in  dibenzobarrelene  which,  pathways  and,  reaction  four  pathway  C(A)  participates  the  the  skeleton,  carbons,  the  di-7r-methane  of  reaction  vinyl  that  aspect  connection  including  Nononly  operating of  the  with  our  diesters  such  as  15  where  Figure  R =  17.  isopropyl  The  Four  or  ethyl.  Di-7r-methane  Systems  in  the  Dibenzobarrelene  Skeleton.  In  order  to  versus  B-I  ents.  Dibenzobarrelene  groups,  and  distinguish  R^ *  formation  R2,  the  the  are  depends  rearrangement. give  B-II,  In  two  vinyl  expected which  Figure  18,  A  and  such  to of  the  the  carbons  compounds  on  regioisomer  between  should as  give the  v i a  15  two  two  reaction  reaction  reaction  v i a  pathways  bear  different  with  two  different  vinyl  carbons  pathways  pathways  A-I  B-I  A-I and  and  A-II  substitu-  different  ester  products  whose  engages or  B-II  A-II  in  the  should  should  give  -38-  regioisomer  B.  rearrangement expected The that  a  to  is  be  mixed  centers  to  t i v i t y  but  on  the  the  us  to  rate  These  exert may  be by  in  on a  a  some  crystallization  Part  of  the  III  of  size  should  step,  which  and  effect  on  thesis  were  branching  remote  the  by-product on  this  perturbation  be  steric  information  regioselectivity  of  the  is  also  s t e p . ^  effects  interesting  the  reaction  negligible  moderate  profound  that  f i r s t  the  substituents  have  obtain  the  studied  cause  just  and  noticed  determining  variation  would  important  allow  determined  homologous  chromophore.  should  diesters  substituents  very  It  the  of  enough  on  the  crystal this  steric  dibenzobarrelene  designed  of  the  so  alkyl  to  the  reactive  from  the  reaction  solution packing  design  is  effects  of  regioselec-  properties. that  it  A  should  substituents  molecules.  COORl  COORl  A  Figure Diesters.  18.  Regioisomeric  Products  from  "Mixed"  Dibenzobarrelene  -39-  Several prepared on  the  mixed  for  to  can  to  the  four  category  In  are  formed  related  the  w i l l  18  we  this  thesis  occur  in  in  a  in  section  of  This  class  solution  with  benzo-vinyl  bonding  stabilizing  effect  reaction  of  of  state  of  from the  at of  of  their  the  the  A and  B  should ester  diesters  four  the  yields  17A  11,12-diesters  compounds  The that  will  Part  as  17A  in  this  this  observation  in  to  17B  the is  give  resemble  photoproducts (Figure  studied  context  of  expected  to  products  (b)  18).  the  such  formed  because  at  (Figure  photochemical  The b i r a d i c a l s  C ( l l ) ,  studies  been  state  favored  above  of  dimethyl  our  not  substituents the  most  of  and  rearrangement  19).  the  with  interesting  largely  mentioned  of  for  direct  has  solid  regioselectivity  be  using  deal  such  and  very  (Figure  each  discussed.  compounds  solution  by  allows  w i l l  diesters  is  be  included  p o s s i b i l i t y  be  VI,  these  should  into  discovered  analyzed  window  products  thesis.  luminescence be  lattice  pathways,  reaction  relative  were  molecular  reaction  different  their  di-rr-me thane  quantitative  C(12)  Four  example.  compounds  (a)  the  this  will  thesis,  explore  because:  expected  IV  intermediates  photochemistry to  of  from  9,11-dibenzobarrelene the  By v i r t u e  crystal  results  thesis  the  the  The  spectroscopic  reaction  of  dibenzobarrelenes  representative a  substituents  excited  Part  the  effects  substituent,  and  ester  the  solid  dibenzosemibullvalenes  ducts  the  reaction.  circumstances  unusual  decided  reactivity.  as  the  and  the  chiral  pathways.  being  Although  before,  these  studied  final  of  the  analyzed  as  10,11-  19).  in  postulated  The  observing  partitioning of  V,  luminescence  on  of  chiral  rendered non-equivalent.  be  diesters  the  by  reaction  Part  diester  of  purpose  given  B-II,  be  the  the  possessing  diastereoselectivity  disymmetry A-I  diesters  of  by the  photopro-  formed This  from should  -40-  offer  the  manner  to  the the  opportunity confirm  ester  our  group  on  quenching aspect, that  studies  and,  (e)  while  -COOR^  group  reactivities contrast  to  to  may the  bridgehead  skeleton could  interest  the  displacements  preparing  stereochemical the  dibenzobarrelene  of  has  -COOR^  the  not  solid  give  the  expected  in  17B  should  be  expected  solid  state  for  been  some  ester  reactivity  on  17A  almost types  from  regiospecific  influence the  that  reactivity  on  this  of  arises  from  should the  the  suffer  position  compounds  and  particular  unaffected.  of  the  a  Quantum y i e l d s  reaction  product,  remain two  may h a v e  in  in  the  information  state  major  (d)  documented.  groups  the  compounds  assignments, position  provide in  these  which  fact large  of  the  Different may  also  11,12-diesters.  COOR2  RiOOC  RiOOC  COOR2 ^COORl  RiOOC  RlOOC  COOR2  C00R2  B  A COORl Figure  19.  9,11-Dibenzobarrelene  Di-w-Methane Diesters.  Rearrangement  of  10,11-  and  -41-  RESULTS AND DISCUSSION.  -42-  RESULTS AND DISCUSSION.  Preparation  of  Substrates.  11,12-Dibenzobarrelene Diesters. The s y n t h e s i s o f t h e 1 1 , 1 2 - d i b e n z o b a r r e l e n e d i e s t e r s s t u d i e d i n t h i s t h e s i s was b a s e d o n c h e m i c a l dimethyl  compound  18  (R  modifications =  Me)  to  prepared  the readily from  dimethyl  d i c a r b o x y l a t e a n d a n t h r a c e n e b y t h e method o f D i e l s procedure  was  (27).  esterification  and  The  by using di-(1)-(-)-menthyl l a t t e r compound was p r e p a r e d  o f acetylene  dicarboxylic acid  acetylene  A l d e r . T h i s  a l s o used i n thep r e p a r a t i o n o f t h e dimenthyl  (R = ( 1 ) - ( - ) - m e n t h y l ) late  accessible  acetylene  d i e s t e r 26 dicarboxy-  by thermal s e l f - c a t a l y z e d  with  (1)-(-)-menthol  by  employing a m o d i f i c a t i o n o f the l i t e r a t u r e ^ 1 procedure c o n s i s t i n g o f n o t using a sealed  tube,  b u t an open c o n t a i n e r  t o heat  t h e two components  together.  Dibenzobarrelene R = Me . R - Menthyl Figure Reaction.  20.  Synthesis  of  Dibenzobarrelene  18 26 Diesters by Diels-Alder  -43-  Two t r a n s e s t e r i f i c a t i o n methods were employed i n o r d e r the  methyl  found t o r e q u i r e l o n g r e a c t i o n  8  Although  this  for  groups  of t r a n s e s t e r i f i c a t i o n  (Figure  21).  The  products  replacement  c o u l d be o b t a i n e d by s t o p p i n g the r e a c t i o n  an  almost  and  the s i n g l e  of  both  transesterification  R  = alkyl)  2  products.  Yields  and of  at a  when i t had  method  double  (R^  only  around  methyl single reached  (R^ = R2 = Me)  s t a t i s t i c a l d i s t r i b u t i o n of starting material (R^ -Me,  method  times (from a few days to almost two  weeks) i t was found to be c o n v e n i e n t  position  exchange  groups o f the e s t e r f u n c t i o n a l i t i e s on 18. The f i r s t  involved a mineral acid catalyzed a l c o h o l y s i s . ^ was  to  •=  R  2  =  alkyl)  40% and r a t h e r  d i f f i c u l t p u r i f i c a t i o n procedures encouraged us to l o o k f o r a second and more e f f i c i e n t method f o r the p r e p a r a t i o n o f mixed  esters.  (1%)  Ri - Et  28  21  = nPr  29  22  -  iPr  30  23  -  secBu  31  24  -  iOct  -  25  F i g u r e 21. A c i d C a t a l y z e d T r a n s e s t e r i f i c a t i o n  o f D i e s t e r 18.  -44-  The  second  transesterification  stepwise procedure dimethyl  shown  in  compound 18 was  the  easily  by  figure  treatment  procedure  o f D i e l s and A l d e r which c a l l s  that  on  faster  Table  I.  of  the  anhydride  The diacid  20  was  than  the  cyclodehydration  f o r treatment o f the d i a c i d  19  anhydride.  f o r m a t i o n o f 20 i n o x a l y l c h l o r i d e i s an i n t e r e s t i n g r e a c t i o n i n  it  seems to f o l l o w an i n t e r m e d i a t e monoacyl c h l o r i d e t h a t  c y c l i z e s w i t h e l i m i n a t i o n o f HC1. required  alcohol  in  order  to  Compound  20  was  isolated  but  immediately  in situ,  treated  with  an excess o f o x a l y l  to g i v e  the  dry  alcohol  to  give  convenient f o u r hours improvement found t o be  since  opened not  chloride,  corresponding  acyl  treated  with  the  e x c e l l e n t y i e l d s o f the f i n a l mixed found  to  be  very  the t o t a l sequence can be c a r r i e d out i n about two  s t a r t i n g from from  the  the acid  diacid  19,  catalyzed  thus  representing  a  applying  this  to  great  procedure. T h i s method was  i d e a l f o r the p r e p a r a t i o n o f o p t i c a l l y a c t i v e compounds. prepared  the  were  These compounds were n o r m a l l y not i s o l a t e d but  d i e s t e r p r o d u c t s . T h i s one pot r e a c t i o n sequence was  compounds  20  a f t e r e v a p o r a t i o n o f the excess s o l v e n t and r e a g e n t ,  appropriate  in  generate the c o r r e s p o n d i n g r i n g  e i t h e r neat or i n dry dichloromethane, chloride-esters.  readily  dissolved  monoacid. The monoacids formed by a d d i t i o n o f a l c o h o l s t o  below.  the simple  o f 19 w i t h excess o x a l y l c h l o r i d e . T h i s  found to be c l e a n e r and  The  based  accompanying  preparation  method was  in boiling acetic  was  used as a s t a r t i n g p o i n t to p r e p a r e the  19 by a l k a l i n e h y d r o l y s i s . The achieved  method  also The  methodology are i n c l u d e d i n Table I  -45-  Table  I. Dibenzobarrelene Diesters  Prepared by Stepwise  Esterifica-  t i o n o f the D i a c i d 1 9 .  R  Me Me Me Me Me Me Me Me Me Me Et Et iso-Pr iso-Pr a)  R'  n-Pr iso-Pr (R.S)-sec-Bu (S)-(+)-sec-Bu tert-Bu n-Pent iso-Pent neo-Pent^ (D-(-)-Menthyl Phenyl iso-Pr (S)-(+)-sec-Bu (R,S)-sec-Bu (S)-(+)-sec-Bu  (S)-(-)-2-Methyl-l-butyl;  a  Compound Melting point 29 103-4 30 124-5 94-5 (R,S)-31 (S)-(+)- 31 91-2 32 128-9 33 liquid 34 63-5 35 75-80 36 liquid 37 180-1 38 104-5 39 72-3 (R,S)-42 122-4 <S)-(+>- 42 133-5 b) 2 , 2 - d i m e t h y l - 1 - p r o p y l .  -46-  P r e p a r a t i o n o f 10,11- and 9 , l l - D i b e n z o b a r r e l e n e d i e s t e r s .  A  Diels-Alder  r e a c t i o n between  (43)] and methyl p r o p i o l a t e compounds  (Figure  was  23).  As  pyl-9-anthracenecarboxylate 9-anthracene  9-isopropyl-9-anthracenecarboxylate  used  as  shown  the  entry  i n Figure  derivative*^  was  f o r the  22,  the  prepared  title  9-isoprovia  the  a c y l c h l o r i d e o b t a i n e d from the c a r b o x y l i c a c i d and o x a l y l  chloride.  1) C2O2CI2 • 2)R0H COOH  COOR  R  Compound.  2-propyl  43  F i g u r e 22. P r e p a r a t i o n o f 9-Isopropyl-9-anthracene  COOR'  Carboxylate  R'OOC  H  COOR  R  R'  2-Propyl  Me  Compound ( y i e l d ) 44  (66%)  Compound  (yield)  45 (23%)  F i g u r e 23. P r e p a r a t i o n o f 10,11- and 9 , l l - D i b e n z o b a r r e l e n e D i e s t e r s .  -47-  Th e i d e n t i f i c a t i o n o f the the  difference  p r o t o n s . ^ The from  the  vicinal  i n the  NMR  diagnostic  significant  isomeric coupling  (Figure  difference  24).  X-ray d i f f r a c t i o n a n a l y s i s regioselectivity  primarily  between the b r i d g e h e a d and  on  observed  between  the  p r e s e n t i n the This  1 0 , 1 1 - d e r i v a t i v e , perhaps on substituents.  based  the in  allylic  10,11-  assignment  was  d i e s t e r compounds the  the b a s i s  reaction of  the  stems  [H(9)-H(12)  and  and  clearly steric  and  9,11-diesters  f u r t h e r confirmed 44  on  vinylic  v a l u e o f the magnitude o f t h i s c o u p l i n g  [H(10)-H(12)] c o u p l i n g  respectively  d i e s t e r s was  45.^  3  favoured  effects  of  by The the the  Figure (B)  24.  Partial  1  H NMR S p e c t r a  of  (A)  9-Isopropyl-11-methyl-dibenzobarrelene  10-Isopropyl-ll-methylDiesters.  and  -49-  PART  I.  The  T H E DI-TT-METHANE  photochemical  substituted 1966.  J  series  of  reported  a  transformation the  it  give  studied  direct compounds  a  of  studies  semibullvalene  the  triplet from  on  singlet  by  the  related led  r e a c t i o n ^  Ciganek  upon  and  25).  a  Almost  Zimmerman,  of  In  the  that  direct  of  in  dibenzose-  mechanism.^  3  its  photochemical  H . E .  rearrangement  states  E.  of  irradiation  (Figure  biradical  di-7r-methane  some  corresponding  photoproducts  specific  their  the  only  di-w-methane  that  solution  the  classical  and  sensitized  gave  now  shown  in  or  to  react  to  later  dibenzo  simple  alkyl  irradiation  to  dibenzocyclooctatetraenes.^  Although following been  a  large  these  view  of  years  on  in  the the  attempted seem  no  It in  the  because too  postulate.^  a  reports  organized  study  of  attempt  intense  environments.1 rearrangement  number  i n i t i a l  o b t a i n e d , ^  rearrangement  may  series  STATE.  dibenzobarrelene  barrelene  is  derivatives  as  I N THE SOLID  of  was  derivatives  of  f i r s t that  derivatives  simultaneously,  studies  was  dibenzobarrelene  mibullvalene  postulate  behavior  analogs  Ciganek  REARRANGEMENT  of  a  media.  lack  activity  state,  molecular within  to  This  possible  deal  studied  of been  made  of  interest  is  developed  the  expectations  the  to  years  in  study  the  various of may  the not  to  reach  of  the  has the  surprising  during  study  required  in  understanding  have  particular,  motions  the  been  reactions that  in  has  great  seems  photochemical  solid  drastic  and  research  seems  the  substrates  last  in few  organized  di-7r-methane have the  been  products  topochemical  -50-  E x p l o r a t o r y S o l i d S t a t e Photochemistry lene D i e s t e r  solutions  Ciganek's 52  was  Dibenzobarre-  18.  Compound 18 was acetone  o f the Dimethyl  report^ detected  (acetone) s o l u t i o n  F i g u r e 25. The  photolyzed f i r s t and  then  in  i n 0.1  the  M benzene, a c e t o n i t r i l e  solid  state.  a s i n g l e p r o d u c t i d e n t i f i e d as from d i r e c t irradiations  (benzene (Figure  and  I n agreement w i t h  dibenzosemibullvalene  and a c e t o n i t r i l e ) and  sensitized  25).  Di-7r-methane Rearrangement o f  the  Dimethyl  Diester  18.  Solid  state  i r r a d i a t i o n s r e s u l t e d i n the f o r m a t i o n o f a p r o d u c t w i t h  g l c r e t e n t i o n time and MS duct.  The  i d e n t i c a l t o those o f the  i d e n t i t y o f the s o l u t i o n and s o l i d  c o n f i r m e d by comparison  solution  photopro-  s t a t e p r o d u c t s was  o f the s p e c t r o s c o p i c and a n a l y t i c a l  further  information  from the p r o d u c t s i s o l a t e d from p r e p a r a t i v e p h o t o l y s e s i n each media. I t s h o u l d be n o t e d t h a t p r e p a r a t i v e p h o t o l y s e s  in  the  solid  state  were  carried  out  from  the  dures  led  to  a  limited  unreacted us  to  diazomethane  conversion.  starting  convert  adduct  material  the  53^^  The  inseparability by  starting  (Figure  normal  of  product  chromatographic  material  into  the  proce-  separable  26).  COOMe  MeOOC  the  COOMe  N-N  COOMe  MeOOC COOMe  52 Figure Diazomethane  A  Derivatization  26. to  striking  Yield  the  observation  was  analytical  irradiations  of  solid  runs.  ($52) *52  w  a  s  ™ 0.2.  available, be  state  measured Although the  significant  photochemical been  reported  by the  The  view  occur  Reacted  of  over  side-by-side  indicated  quantum  absolute  reactions. to  that  triplicate  apparently in  Partially  Chromatographically Separable  state the  of  yield in  solid  the  low  as  state long  solution  formation solution  state  state  Adduct  conversions of and  quantum  efficiency  efficiency  solid  periods  of  benzene  solid  high  Some  larger  Diester  of  is  many  few  with  53.  and in  solid  the  case  diester found  yield  photochemical as  18  52  to  be,  is  not  considered solid reactions  months.68,20  to  state have  -52-  On  The  True  One the  of  Solid  the  internal  ogy*^  to  and  the  expected points,  diester  18  guarantee amounts  has  a  heat  relatively  intense  to  practical diminish  room  indicate methods  a  techniques  energy of  heat  of  melting in  the  during of  the  the  internal  also  be  the  low  point event  of  one  reaction  and  fluorescence conversion implemented  of  regions  in with  (fluorescence The  dimethyl  which  should  significant  Furthermore, the  finding  diester  quantum in  concom-  compounds  having  irradiation.  should  by  160-1°C,  of  of  methodol-  liquid  yields. of  The  form  state  luminescence  quantum  is  l i g h t - i n i t i a t e d  occurring  reactions  high  in  rearrangement  in  reaction  reaction.  solid  reaction  display  the  in  important  temperature  can  of  microscopic  melting  low  photochemistry  of  also  efficiency  state  di-jr-methane  low  evolved  high  seem  to  nature  source  the  state  generation  be  relatively  relatively  62)  to  solid  state  a  having  The  and  resistance of  of  which  phosphorescence)  the  the  of  excited  constitute  of  Rearrangement.  solid  the  apply  melting.  the  aspects  true  of  possibility  is  melting  to  study  crystal  crystal  the  may  order  the  eliminate itant  of  dissipation  In  of  Nature  important  conversion  reactions.  low  most  determination  radiationless  the  State  18  order  to  of  (see  yield.  the a  page  Several detect  and  melting:  a)  Microscopic  inspection  b)  Photolysis  to  very  low  conversions.  c)  Photolysis  at  very  low  temperatures.  d)  Derivatization  to  very  of  photolyzed  high  melting  single  point  crystalline  compounds.  samples.  -53-  e) and  D e r i v a t i z a t i o n to compounds t h a t may  display different  solution  s o l i d state reactivity.  T y p i c a l r e s u l t s o f s e v e r a l experiments c o v e r i n g a s p e c t s three  categories  are shown i n Table  the rearrangement c o u l d s t i l l reaction achieve  efficiency,  as  judged  found  from  the  to decrease  -70°C.  barriers  experimental between  data^  the  that  describe  that The  time r e q u i r e d to  significantly  temperature. T h i s o b s e r v a t i o n i s i n agreement w i t h  c a l m o d e l s ^ and thermal  however,  first  s a t i s f y i n g to f i n d  occur a t temperatures as low as  a c e r t a i n c o n v e r s i o n , was  decreasing  I I . I t was  o f the  theoreti-  existance  of  v a r i o u s r e a c t i o n i n t e r m e d i a t e s . The  low  temperature i r r a d i a t i o n s were h i g h l y s a t i s f a c t o r y not t h e i r h e l p i n g to accumulate evidence  the  with  only  because  of  a g a i n s t the p o s s i b i l i t y o f m e l t i n g ,  but a l s o because a f a s c i n a t i n g luminescence b e h a v i o r , i n a l a t e r s e c t i o n o f t h i s t h e s i s , was  discovered.  to be  dealt  with  -54-  Table State  II.  Analytical  Photolysis  of  18  in  Solution  and  in  the  Solid  3  Sample  A ,nm  T°C  Irrad.  % Conversion  time  Melting  1.  0.1  M CH CN  >290  20  75  min  3.8  -  2.  0.1  M Me C0  >290  20  75  min  2.5  -  3.  Crystalline  >290  20  min  3-15  No  4.  Crystalline  >290  20  20-25  Yes  5.  Crystalline  337.1  20  6.  Crystalline  337.1  -40  7.  Crystalline  337.1  8.  Crystalline  >200  a)  Irradiations  3  2  quartz  The  the  we  A >  f i l t e r e d output  Irradiations  as  at  unique  w i l l  true  at  also  solid  337.1  solid see state  290 of  ,a  nm  state below, nature  5-75  1-10  h  min  1  10  min  5  No  -70  40  min  2  No  20  30  min'  15  Yes  200  were  and  1-10  A >  450 W medium were  realized  with  of  contributed the  the  of to  <30  the  presure Hanovia  stereoselectivity also  done w i t h  -  :  Pyrex  laser.  ii i n s y m m e t r i c a l  rearrangement.  more  or  lamp;  nitrogen  gain  No  compounds  confidence  in  The  Limiting  When i t  was  C o n v e r s i o n on  single  found  crystals  that  the  of  solid  irradiations  yellow  to  coloration  photoproduct. colored  of  substance  18  State  were  were  became  there  may  30% h a d  not  exists  act  as  by  be  the  of  been the  after  reached.  attributed  at  the  to  that  later  18.  at  337.1  nm  a  limiting  Solution  development  possibility  f i l t e r  Diester  irradiated  unreactive  accompanied  could  Reaction  exhaustively  approximately  which  Although  Solid  crystals  conversion state  up  the  of  any  a  slight  detectable  traces  stages  and  of  of  some  the  reac-  70 tion, the  ^  two  limiting The  regions  of  of  principal  conversion  f i r s t  reactivity  a  other  and 18  of  could  arise  crystal.  photochemical  reaction  get  with  light  with  loss  (i.e  entry In  mately  8  crystal  of of  the  resonance  and  through.  8,  case  unreacted  of  mol"^  an  of  this  of 1.2  value  of  18  18  the of  and  an  cm"^the g  the  fact  bulk  of  understand  the  is  melting  that may  the  inside  that  irradiating a  with  by  extinction  was  measured  nitrogen  cm"  approximate  crystal  in  to  for  UV e x p o s u r e  wavelengths  control  to  in  limiting  the  deepest  order  crystal  to  have  the  light  crystalline  sample  product  occur  saturation,  near  the  surface  II).  wavelength density  relates  absorbed  order  explanation  limited  consequence  compound  liters  combining  calculate  Table  from  in  18.  occurring  topochemical  analyzed  possible  This  The  strongly  were  diester  simplest  the  must  factors  3  we the  get  laser a  above  penetration naive  in  coefficient  of  methanol  solution  (337.1  crystal  application  of  By  concentration  extinction depth  nm).  approxi-  of the  of  coefficient about  0.5  at  the  using  a  3.75  M,  we  mm f o r  Beer-Lambert  can the law.  -56Analysis  of  52  other  on  the  wavelength of  18  and  concentrated hand  revealed  (approximately 52  solution,  in  it  the  can  transparent  at  assumption  is  be  the  laser  correct  that  reaction  tions in  is  can  the  in be  photoproduct having  does  state aided  the  crystalline  depth  phase  able  pathways  of  ^ a n d  the  Excited  Accumulation  of  the  Photoproduct.  of  the  excitation  strongly  fate  dependent  situations the  can  molecules  impurity anthracene  of  on  be a  the found  crystal  compound. crystals  One  energy  where are  to  a  absorption  spectra  those will  Why i s  limited  example  the  an then  in  the  explana-  perturbations compound  via  possibility  solubility  of  in  the  17 39 '  organic  of  Crystalline  crystals  suppressed from  l/10,000th  the parts  is  Some  normal e x c i t a t i o n  comes  have  molecule  crystalline from  this  it  possible  composition.38-41  the  If  should  from  in  essentially  nm).  every  Two  obtained be  light  originate  Channels  in  shorter  (337.1  i f  second  completely  with  the  at  product  a  proceeds.  the  the  Decay  sample  such  doped  can  material.  State  starting  the  photon?  presenting  of  The  a  one  Perturbation  that  completion  absorb  di-w-methane  photoproduct  reaction  to  starting  that  similar  expected  go  3  the  wavelength  first  product  the  are the  the  to  The  decay  of  be  as  c h a n n e l s  final  that  not  anticipated.  excited  Assuming  crystals  can  of  UV-absorption t a i l  excitation it  principle  solutions  nm).  concluded  penetration  the  a  310  reacted  increasing  crystal  methanol  by  decay a  18  by  known  to  spectacular channels  minor  fluorescence of  be  of  guest of  or  thin  tetracene.  73  -57-  Irradiation by  the  state  mechanism.  molecules  Phenomena  possessing  as  to  energy  system  there  to  a  the  find  i t s e l f again.  conditions  can  to  energy  The  take  pair.  exchange  and  the  and have  some  ties  differences  a  an  energy  concern that  could  or  be  energy  energy a  been  on In  w i l l  of  example transfer  among  solid  give  products  close  to  one  being  called  decay  no  channels  from  there  from  an  with  extremely  molecule  principle "hop"  and w i l l  are  primarily  resemblance  molecule  trap"  doped,  results  sites.  foreign  one  to  a  in  molecule migrating  of  the  If  energy  longer  be trap  a  always  e x c i t o n . ^ lower  the  a  levels  able are  to then  over. mechanisms some  These  distance.  not  mechanisms,  interesting the  do  favorable  F o r s t e r mechanisms  between  donor-acceptor  also  unimolecular  through  donor-acceptor  the  pure  property  excitation  "energy  transfer  operate  some  absorbed  detection  represents  crystals  excitation  has  an  of  identical  the  in  exclusive  efficient  raise  whether  This  3  giving  delocalize  but  " ^  many  encounters  very  mostly  disallowed.  the  "particle"  almost  t r a p p i n g mechanisms  other  exciton  Other  8  wavelengths  situation  should  general, 3  of  an  a  reaction  probability that  migrating  in  are  this  finite  This  w i l l  in  localize  particle.  it  a  energy  t r a n s f e r .  to  where  in  interesting  as  since  crystals  impossibility  exists  This  topochemically  Molecular  light  resulted  such  efficient  classified  with  perturbation through  photochemists,  prone  crystals  fluorescence.  excited  state  these  anthracene  tetracene of  of  two  features  One  of  concerns  Forster,  or  of  to  respectively,  mechanisms the  exciton  referred  contrasts.  Whereas  need  delocalization the  prospective  as  the  electron  share  some  similari-  the  their  main  practical  dependence  dipole-induced,  on  the  energy  -58-  transfer  operates  transfer  by  electron  donor-acceptor molecular overlap rate those  almost  by  donor  exchange,  the  Both  therefore state  solid  state  aid  ^  In  are  the  there  are  the  irradiation, w i l l  be the  52)  starts  no  the  the  not  operates  in  t r i p l e t  the  of  on  acceptor  depend  on  of  as  two  the  or  the  three  spectral  absorption. the  case  rate  values  order  depend  the  of  absorption  The  intensity t r i p l e t  of  energy  probability  is  unreactive  the  added  interactions impurities  photophysical  in  the  composition  of  case  of  the  have  of  studies  becomes  impurities  the  crystal  to  to  follow  is its  (which  accumulate,  (Eq.  8-9)  pairs.  the  been  in  where  dynamic  sample  studied  variable the  crystalline  a  of  from 18.  diester  18,  composed  mainly  normal  decay  may b e  some  new  concentracontents  of  photoreactive  variable.  composition  If  the  the  at  the of  is  on rate  energy  of  photoproduct  starting (Eq.  undetected  the  may  i n i t i a l  channels  heteromolecular  depending  excitation  manner  pathways  state  Assuming determined  conversion.  donor-acceptor significant,  of  these  other  photoproduct  operate^-*  decay  to  constant,  case  able  When  the  sample  percent  In  with  contrast  samples  the  does  to  excited  3  negligible  than  and  50-100 A ,  as  mechanisms  however,  ground  to  more  emission  intermolecular  that  to  increases  large  negligible).  systems  by  drops  A).  (and  as  exchange  Many  t i o n . the  the  transitions where  distances  (-15  diameters  electron  transfer  the  distance  between  of  over  energy be 52  of  2-7,  the  thereby  the  which  Figure  27).  other  than  pathways  transfer  f i n a l l y  of  material  species  decay  nature  stages  may  start  prospective happens  dissipated quenching  the  to in  be an  normal  -59-  1)  18  >  2)  -^lS*  >  1  18*  Light  18+hv^  or  heat  absorption  Fluorescence  by  or  18  internal  conversion. 3)  ^18*  4)  ^18*  >  18*  >  5)  3  +  18  >18  3  +  18*  1  Homomolecular  18*  Intersystem  18+hv2  or  heat  singlet  transfer  crossing  Phosphorescence  or  intersystem  crossing. 6)  18*  3  7)  >18+ >  -->  3  -->  18*  Homomolecular  52  Di-7r-methane  t r i p l e t  transfer  rearrangement  8)  1  18*  +  52  >  18  +  1  52*  Singlet  quenching  by  52  9)  3  18*  +  52  >  18  +  3  52*  Triplet  quenching  by  52  11)  Crystals  It  of  >  52+hv  52*  >  52+hv  27:  Photochemical  Reactant  should  account  decay  *52* 1  Figure  be  should  present  for  and  3  4  or  heat  Deactivation  of  singlet  52  or  heat  Deactivation  of  t r i p l e t  52  Activation  and  Decay  Processes  Available  to  18.  pointed  only  channels  however the  18  18  10)  11  +  a  out  that  limited  discussion.  useful  processes  number  interactions.  prove  the  3  8  "^  3  within  of  >^ the  a l l  shown  the  This merely  in  equations  possible  excited  oversimplified illustrative  2  to  state picture  context  of  -60-  The  rate  function the  of  the  various  electron w i l l  constants  transfer  exchange). ^•^ 3  on  the  We  limiting  concentration  of  therefore  transfer  reaction  Two  (Eq.  sets  capabilities the and  (i.e.  yield  study  the  conversion  a)  as  a  and  in  function  an  of  the  were  realized  angle  that  due  to  geometry.  The  spectra  laser.  the  as  of  of 52  and  52  the  parent  possibility  to  within  our  by and  in  enough  a  induced 18  which  be  required  dipole  after  large  performed These  spectra  measurement as  the mask  consisted of  of  the  photolysis  after  they  by  causes  variations  and  52  to  that  a  rates  of  the  rate  instrumental of  measuring  crystalline the  relative  dependence  of  before  18  quantum  the  percent  time.  Measurements.  spectral  before  trap,  reached  become  expressed  Powdered  K  be  were  the  monochromator.  sample  and  expected  molecules  of  possibilities.  emission  in  9)  18  be  distribution  aware  could  and  between  phosphorescence  reaction  Measurements at  8  these  and  Luminescence  detection  52  Eq.  irradiation  of  of  between  and  be  experiments  fluorescence after  to  9 would  (exciton  distance  have  and  7).  of to  mechanisms  The  3  8  distance  concentration  crystal.  energy  equations  intermolecular  energy  depend  for  front most  samples  scattering of  were  the  surface  specular were  solid  irradiated  reflection  used  problems  illumination  in  order  resulting  samples at  were  -20°C  to to  from  miss  the  minimize variations  obtained  with  and  the  at  77  nitrogen  The  uncorrected  consisted  of  a  reaching  a  of  samples  solid  fluorescence  broad  structureless  maximum n e a r  400  (Figure  solution.  nitrogen  laser  resulted  dependent  spectral  the  In  order  fluorescence  after  few  minutes  Although lyzed  to  less  intensity however, Besides  the  at  samples  to  band  assigned  rearrangement  were  effects  the  based  fluorescence the  a  new the on  of  the  fluorescence  (only  detected  at  sample  had been  irradiated  clearly  perturbations evident,  no  of  largely  77  into  K)  the  the  to  an  end  were  the  found  of  clearly  in on  presence  470  new  band methyl  the  other  to  the  a  evident.  di-7r-methane The be  latter  reproduced  tetrahydrofurane. hand,  strong be  evident, 28).  the  of  its  (Figure  intensity, nm w a s  photo -  unaltered,  conversion  A relatively was  of  samples  changes  fluorescence  spectrum,  nm  were  in  phosphorescence  at  Although  envelope  15%  measured  intensity.  V  came  could  that  the  photoproduct,  fact  the  the  stable  methyl  temperature  Part  52.  to  after  with  dibenzosemibullvalene  related 550  to  the  samples and  and  spectrum in  had  Additional  increase  to  nm  obtained  in  the  remained  52 w a s  spectral  to  350  18  temperature.  maximum a r o u n d band  solid  changes  ambient  about  complicated  due  these  photolyzed  with  be  increased.  detected  product,  is  be  the  that  discussed  conversion  found  the  to  at  fluorescence  w i l l  -6-8%  have  in  the  the  of  than  We  Changes  (these  dark  starting  similar of  polycrystalline  series  of  fluorescence  the  a  shape  new  when  the  previously  assignment  very  r e c o r d e d when  in  of  Qualitatively,  the  was when  in  observe  was  band  Irradiation  changes to  nm.  28) was  tetrahydrofurane  thesis).  spectrum  were  mainly  phosphorescence  considerably  quenched  (Figure 28). normal  definite  decay  conclusion  channels of  of  these  diester effects  18 in  -62-  reactivity  can  be  follow  immediately  of  stable  the  large  in  the  with  the  cence  quenching  of to the  the expect  that  the  state  through far  there  photoproduct in  is  should  in  that  phosphorescence  accumulation  of  the  be  is  of  no  may  triplet  result  product.  an  seems  this  spectral  in  band  at  from  that  view  of  spectral  nm).  is  associated  is  because  reasonable levels  possible  environmental  The  Phosphores-  absorption It  effect rather  unlikely It  that  changes.  directly  f i r s t  (550  the the  intriguing.  energy  region.  changes  seems  aspect  somewhat  transfer  location  It  these  intensity,  reaction,  spectral  V).  moderate  accompanying  energy  the  (Part  rather  phosphorescence  triplet  studying  irradiation  conversion  relatively  decrease by  after  without  photoproduct  percent  decrease  reached  that  effects  of the  caused  -63-  350  400  450  500  550  600  650  Wavelength  450  500  550  600  28.  Polycrystalline Nitrogen  Laser.  Uncorrected 18  at  77  K  Fluorescence  (a)  Before  and  and  Phosphorescence  (b) A f t e r  (nm)  650  700  Wavelength  Figure  700  (nm)  Spectra  Irradiation  with  of the  -64-  b) of  Conversion  Diester  of  by  the  measurable  since  excited  Wagner,^  is  the  under  photochemical  parameters a l l  they  absorption  the  of  probability  of  light that  w i l l  process  in  (unimolecular)  one  starting  produced by  amount  of  diester  disappearance  absorbed  the  quantum  state  kinetic  of  an  the  is  the  ideally  i n t e n s i t y . ^  undergo and,  the 3)  the  excited  per  *  constant  I  interactions  yield  2)  instead  state  that the  that of  starting  product  is  out  photoreac-  probability  the  for  reaction  state,  product  alter  quantum  of  the  expected  to  accumulates.  concentration, duration  unit 18  time. is  d[18],  one  uses  a  the  then  The  quantum y i e l d  and light  d[18]/dt  reacting is  the  for  the  b y : ^  Eq.  quantum y i e l d  of  dt,  given  a  i f  pointed  primary  no  species  However,  excited  If  in  As  probability  material.  converted  =  the  final  i r r a d i a t i o n of  reacting  1)  the  the  constants  photochemical  to  change  -d[18]/dt  $  Reaction  rate  it  photoproduct  the  18  w i l l  the  processes.  required  make  bimolecular  the  species  w i l l  excited  between  question,  probabilities,  measures  true  particular  the  the  material-photoproduct  where  of  conditions,  probabilities:  state  the  as  a  excited  intermediate to  are  the  reaction  If  Quantum Y i e l d  state  balance  for  produce  any  constant  the  several  for  back  steady  quantum y i e l d  necessary  remain  Relative  activation-decativation  tion  above  the  reactions  reflect  state  product  reverting  of  18.  Although yields  Dependence  12  I  is  the  average  source  with  constant  a  intensity  and  we  assume  that  I  is  a  directly  proportional  to  [18]  we  have  that:  d[18]/dt  where  k  terms  a  w i l l  p  that  be  account  a  for  absorption  coefficient  Clearly,  plot  a  the  decay  that  those  In  of  homogeneous advantage by  30  at  1640  that  time  of  10  order  decay  although When  cm"^.  min. of  of The  samples to  be  that  no  bending  log[18]  vs  vinyl were to  a  a  After  decrease a  were  plot.  in  repeated over  a  in  29  manner  reproduciin  additional  material  consumption  a  of  the  total  indicate  for  starting periods  irradiation a  clean  quantum y i e l d ,  reaction  value  a  quantum  absorption  benzene  similar  a  the  photolyzed  give  the  such  photolyzed  was  conversion  in  unless  18  constant  the  decrease  occurred t  this  line  the  i n i t i a l l y  as  yield.  in  offered  to  the  maximize  absorption  3 min  flux,  yield.  starting  interpreted  likely,  observed  of  Figure  indicates  experiments  diester  in  conversion.  same  and  shown  20%  less  up  quantum  includes  quantum  straight altered  methodology  that  photon  reaction  a  are  problems  IR  results  the  corresponding  the  to  is  reaction  the  the  13  constant  laser  give  state  determination  18,  value it  This  extended The  should  scattering  rate  the  nm a n d  excited the  order of  337.1  time  in  the  Eq.  f i r s t  measurements  decay  were  approximately slope  reflect  allowing  sec  the  vs the  minimize  the  [18]  p  at  KBr m a t r i c e s . ^  of  a  intensity 18  of  these  monitoring  material of  to  the  log[18]  changes  - k  complex  of  channels  order  b i l i t y  of  =  up  decrease yield  to in (or,  coefficient).  solution  conversion  first  range  it in  was the  The well  large  as  indicate sible  the the  (at  diester  conversion  range  fluorescence unlikelihood  least  of  and  of  constant the  energy  uniquely)  for  solid  quantum  phosphorescence  transfer  the  state  results,  mechanisms  limiting  yield,  being  conversion  of  seem  as to  respon-  crystalline  18.  C  o  V)  2.0  I-, CD >  c  o  1.9  u o o O i-J  1.8 1.7  i  i  2  4  6  8  10  Irradiation Time (min )  Figure Time a  29.  Plotted  Function of  Consumption of as  a  First  Order  Conversion).  Diester Decay  18  as  a  (Variations  function in  the  of  Photolysis  Quantum Y i e l d  as  -67-  Mechanlcal  The  Effects  presence  mechanical of  the  >  mismatch  and  that  the  factors  in  reactions  product  from  a  conversion from  an  value  may  increase  consequence  of  also  in  the  more  size  of  photolyzed  aimed  0.2  x  come  from  internal  product  through  in  examination  of  in  including  some  the  could  be  they  could  randomly  detected be  much  test  as  a  for  x  but  mm  nitrogen that  in  the  a  a  stress  accumulat-  in  were  3  laser  crystals along the  for  of  on  a  min.  extreme ( 8 x 4 x 2  the  with  page a  the 55).  volume.  out  ease. mnr)  to The  be  on  mechanical  an  of  18  approxi-  fiber  and  size  was  light  was  Microscopic change  It  was  noticed  number  of  cracks  of  melting  No  signs  extremely  same  were  stress  remarkable  large  of  3  crystal  that  shown  dioxide  crystals  transparency. a  3  glass  The  showed  entire turned  of  samples  (see  displayed  crystals  crystals  loss  carbon  internal  single  guaranteed  photolysis  their  with  15-20  crystal  after  of  has  kinetics  peresters. of  product  structural  McBride  and  inspection  mounted  principle  entire  and  crystalline  the  dependent  oxygen  texture^  limited  from  involvement  visual  significant  fractured larger  a  upon  peroxides  Single  0.2  conversion  the  a  environment.  generated  change  crystals  photolyzed  distributed  when  to  with  resulting its  the  crystalline  0.5  parameter  texture  radicals  included  the  and  during  saturation.  with  c r i t i c a l  getting  the  associated  interactions  product  single  to  directly  operation  manifested  photolyzed  is  the  saturation  relaxation  made  as  steric  of  Experiments  that  Conversion.  results  factor  between  extrussion  a  limiting  lattice  This  J  solubility  mate  a  Limiting  oo  ing.  the  of  effect  crystal  or  these  and  fragile  observations  photolyzed.  as  were Figure  -68-  30 the  presents  example  di-isopropyl From  limiting to  an  the  limited  these  of  compound  results  conversion  mechanical solubility  we of  effects of  the  one 23  such (Pbca  experiment  modification,  tentatively crystalline of  the  carried  conclude 18  is  that  largely  increasing  photoproduct.  see  on  PART the  (if  internal  We p r o p o s e  out  not  the  of  II).  phenomenon  stress  that  crystals  of  uniquely) caused  a due  by  a  di-7r-methane  •I o rearrangement transformation.  of  crystalline  18  is  a  largely  non-topotactic- 1  0  Figure  30.  Photographs  (Pbca  Modification)  scale  is  shown  in  Before  both  of  a  (top)  pictures.  Single and  Crystal  After  of  Diisopropyl Diester  Photolysis  (bottom).  A  1  23 cm  -70-  The  Crystal  Many the  and  reactions  principal  view  Molecular Structures  is  a  Examples  studied  variable  to  c r i t i c a l  come  to  absence  of  of  mind  occur.  di-7r-methane  system  is,  reaction f i r s t  or  be  starting  The indicates 3  material  X-ray that  the  Wireko,  dynamic  and  of  the  molecular the  NMR s p e c t r u m  A l l Fred  the  (7  X-ray  in  average lines)  crystal  Department  of  behavior  no  2  v  symmetry longer  structure Chemistry,  step  The  state  is  the  inferred  exists  in  U.B.C.  for  hydrogen  by  not  reaction  to  dibenzobarrelene approach required  the  expected of  was  3 3  31  solution solid  of of  state  Figure  the  C12-C10a,  design  therefore  (see  for  occurrence  in  or  (but  (C12-C4a,  work  of  olefin  presence  the  this  in  the  elucidation  2n  intermediates.  shown  that  point  primarily  excited  biradical  18  +  The  distance  31).  of  2TT  r i g i d  from  so  c e n t e r s . ^ • ^ > ^ > ° ^  is  constant  of  postulated  structural  » ° ^  the  bonding  solid  0  cases  of  (Figure the  '  n  bonding  structure C  ,  designed  photochemical  geometry  essentially  framework  and  the  departure  benzo-vinyl held  on  these  The  been  mentioned  c r i t i c a l  35).  rearrangement on  in  rearrangement  is  have  reaction  c o m p o u n d s .  some  page  the  dibenzobarrelene  dependent  ^• C  step,  two  studies  complete  on  Cll-C9a),  di-7r-methane  with  a  mechanism  reaction  Cll-C8a r i g i d  however,  from  18.  chemical  repeatedly  reactivity  associated  a  state  between  carbonyl  state  Diester  solid  from  the  and  exclusively) The  study  from  excited  solid  the  distance  cyclodimerization^ * ^ » ^ abstraction  in  of  state.  the the to the  ' ^* 0  clearly  from  the  As  carried  out  by  suspected, step  were  molecular groups bond. the and  the  X-ray  a l l  conjugate  vinyl  to  be  results to  disymmetry  dihedral the  found  symmetry  The  derived  angles double  a and  benzo-vinyl nearly  from  the  different the  between bonds  degree the  of  the  the  same  (2.43  A).  fact  that  the  two  extent of  mean  [torsion  distances  with  the  conjugation planes  angles  of  the  f i r s t  A  solid carbonyl  central are two  reaction  vinyl  state ester double  determined carbonyl  0(2)-C(13)-C(ll)-C(12)  by  groups and  0(4)-C(15)-C(12)-C(ll)].  Figure Diester  18  31:  Stereoview  of  the  Molecular  Structure  of  the  Dimethyl  PART  II.  It  STUDIES  was  recognized  di-7r-methane compounds  was  the  rearrangement  controlling  their  requires solid  factors  may  structures  order  the At  solid  the  to  same  the  time, of  reactivity.  involved necessary  DIESTERS.  explore  state  identification state  be  are  in  in  required.  the  DIBENZOBARRELENE  that  rearrangement  of  molecular  ON S Y M M E T R I C  the  study  generality of  a  the  detailed  the  factors  Since  different  extents,  in  order  analyze  to  large  the  number  description that  crystal  to  of  may  lattice  be and  variations their  of  of  respective  contributions.  In  order  to  tives  available  state,  several  studied  and  compounds (21),  some  to  the  symmetric their  studied  and  in  this  the  and  their  of  the  be  X-ray  turned  diesters  of out  different experiment.  The  the to  their  obtained  diester  (23),  isooctyl  alterna-  in  the  solid  photochemistry  when  possible.  derivatives:  di-sec-butyl  be  derivative  crystalline  and  23  turned  diesters  24  and  22  and  analysis.  crystal  skeleton  prepared,  the  achieved  prisms  diffraction  were  was  21,  studies,  opaque  series  structural  diester  structures  diisopropyl  crystallization  diffraction  crystal  were  the  (24),  The  diethyl diisooctyl  (26).  exception  series  diesters  this  regarding  dibenzobarrelene  (22),  dimenthyl  With  information  X-ray  di-n-propyl  (25)  to  gain  forms  X-ray  flakes  out  21  (dimorphs^) structures  a l l  at  the  ambient  relative  ease.  to  excellent  be  of  crystallized  respectively  Compounds  crystal  solids  with  26,  25,  and  23  which were  depending of  from  the  were  found on two  the  diesters  temperatures  While  crystals  quality  ethanol,  occur  for  proved  unsuitable to  in  in  for two  crystallization  dimorphs  of  the  diethyl  and  structure  diisopropyl diesters  of  including  the  the  appropriate),  di-n-propyl melting  is  and  23  compound 22.  points  presented  21  in  and  Table  were  obtained  A summary o f  space  groups  of  along  this  each  III.  III.  Compound 18  a)  Symmetrically Substituent  Substituted (R)  Dibenzobarrelene  mp(°C)  Space  group  PT  Me  160-1  21(1)  Et  93-4  P2 /c  21(H)  Et  97-8  P2 2 2  22  nPr  72-3  PT  23(1)  iPr  145-6  Pbca  23(11)  iPr  145-6  P2 2 2  24  sBu  95-6  b  25  iOct  liquid  -  26  Menthyl  147-9  b  a  Diester  1 was  studied  in  the  previous  1  1  1  section,  b)  1  1  1  1  Not  the  information  compound  COOR  Table  with  (where  -74-  Photochemistry  A l l by  direct  valene to  the  and  with  giving  only  measurements  was  rise  the  mass  which  only  racemic  one  glc  forms.  centers  them  three  independent  groups be can  and  expected be  the  to  be  formed  separation  evidence  for  the  spectrum  consisted spectrum  of  approximate  the  two  The  up  to  four  2  products  the  and  was  separated  further  which  of meso  five  several  compounds  solvent  systems,  While  the  glc  of  was  the  55:45  signal  split was  made  which  chromato-  trace  a  can  tic  glc  in  only  sec-butyl  stereoisomers^ Although  and  chiral but  the  These  mixture (R,S-  skeleton), in  this  although  a  the  in  attempt  since  in  peaks  resolution  the  two  pairs.  found  or  structures  sample,  possess  structure.  in  mixtures.  C(8d), No  expected  composed  different  achieved  was  analysis  comment  and  elements,  <= 8  3  found  18.  products  enantiomeric  be  noticeable  1:2:1.  the  presumably  chiral  photolysis  at  with  dibenzosemibullvalene  or  were  identification  elemental  sec-butanol  was  solution  dibenzosemibull-  and  additional  photolysis  the  not  poorly  hydrogen ratio  in  Their  S,S-di-sec-butyl-23)  in  different  presented  cyclopropyl  signal,  in  could  of  deserves  in  rearrangement  diester  dibenzosemibullvalene  differentiated  graphic  NMR  in  consistent for  photolyzed  corresponding  products.  racemic  disymmetric  one  The  were  spectrometry  24  and  S,R-di-sec-butyl-24) of  series  di-w-methane  obtained  with  (R,R-  (three  the  were  compound  prepared  to  from  previously  di-sec-butyl  this  detectable  NMR, F T I R ,  data  of  irradiations.  expected  the  the  material  diesters  sensitized  by  mass  The  of  symmetric  as  supported  and  Solution.  derivatives  form  exact  In  and  the  ratio,  to  the  mixtures the  assigned  into  in  three  -^H NMR to  peaks  separate  the of this  mixture  or  to  quantify  Photochemistry  The  in  generality  confirmed  when  we  manner  similar  carried  to  seemed  either  observed  solution  had  results  w i l l  The  be  of  identified of  in  X-ray  the  of  or by  a l l  the  than  State  Diester solution. tendency  accompanied  state  various  di-7r-methane  the  18.  photoproducts.  by  of  crystal  structural  structures  solved  glc-MS with  solid  features  and  some  of  the  in  the  a  were  conversion The  products  and  NMR  data  state  other  was  reactions  further  glc,  the  reacted  melting.  mixtures  discussing  state  since  the  rearrangement  diesters  Solid  30%,  reaction  Before  detail,  Molecular  21  was  Crystals to  hours.  sometimes  form  new  the  by  plate-like  laminar  to  of  crystallized  with  Repeated  found  Structures  aggregates  solid  crystal state  slow  were  crystallizations give  Diethyl  from  the  photochemi-  compounds  relevant  batches  The  material  remarkably  well  developed  faces  and  These  materials  were  found  the  that was  edges to  (mp  easily  under  Diester  that  details  21.  evaporation  morphology  morphology.  (97-8°C).  the  crystalline  about  comparison  solid  crystal  state  crystalline  less  products.  more  solid  that  that  of  analyzed.  Solid  24-48  to  amounts  State.  the  observed  isolated  their  of  d i f f i c u l t  data  relative  Solid  conversions  were  spectral  cal  the  the  be  93-4°C) a  and  a  period  of  over  same  conditions  obtained a  ethanol  grown  showed  and  «=>  from  remarkably as  large  were  different  prisms  with  different  melting  point  dimorphic^  and  their  -76-  structural  differences  spectroscopic material  was  The  and  group  A').  The  possible  P2^/c  two  crystal, present  and  equal  substituents asymmetric angles  to  is  dihedral  for  amounts.  (Figure  angle  varied  be  The  s-cis  with  the  substituents, the  A)  conformation two  ethyl  can  carbons  other  from  which  the  to  chromophore one  out  and  maintain  4.42° in  for  this  angle  of bond.  The  molecules  also  be  described  as  a l l  in  approximately  the  the  same  can  the  torsion molecules angles the planes  A  and A '  modification a  perfectly  other  is  angle of  be  in  270°  the  ethyl  .(Figure  by  angles  relationship. group  a or  described  torsion  carboxyl plane  in  define  to  the  conformation A and A ' ,  ester  mean  (torsion  anti-periplanar having  the  that  C(13)-0(1)-C(14)-C(15) an  are  torsion  bond  while  conjugation  molecule  of  crystalline  0 ° )  absolute  bond  close  and  The  molecules  very  A  molecules  The  21.  axis.  at  double  double  carbonyl  (torsion  in  each  two  248.62°.  carbonyl-vinyl  6.56°  similar  same  0(4')-C(16')-C(12')-C(ll') to  of  monoclinic  screw  changes  carbonyl-vinyl  249.34°  double  the  the  of  0(2')-C(13')-C(ll')-C(12')  C(16)-0(3)-C(17)-C(18)  (molecule  of  either  (molecules  fold  enantiomers  structures  and  nearly  is  two  conformational  The  unit  and  C(11)=C(12) which  approximate  in  posses  minor  possessing  is  to  both  the  conformation  that  found  of  solutions  crystallized  asymmetric  were an  ethanol  from  ene-dioate as  per  crystallographic,  c r y s t a l l i z a t i o n  vary  the  slightly,  conformation 9  between  described  conjugated  7  Only  I,  their  since  32a).  instance,  respectively.  9 0 ° )  molecules  racemic  Selective  form  by  in  concentrated  molecules  differentiated  unit  of or  related  0(4)-C(16)-C(12)-C(ll)  can  seeding  two  be  manifested  properties.  0(2)-C(13)-C(ll)-C(12)  and A ' ,  also  clearly  material,  with  however, in  by  independent  configuration  A  chemical  plate-like  space  were  and  32a).  This the  The the  prisms  chiral  The  space  molecular  significantly (Figure  the  out  of  The the of  group  found  with of  from  most  that  of  form  almost  the  double  21 in of  bond  groups.  diester per  in  this  this  structure  and  double  C(16)-0(4),  the  b o n d . ^  and  the  were  also  by  the  of  form  having  one  and  structure  other  was  modification  angles the  in  unit.  dimorph  P2^/c  to  packed  asymmetric  characterized  conjugated  21  the  torsion  Similar  grossly  the  molecule  features  central  group,  one  observed  was  perfectly  with  carbonyl  II  contain  diester  salient  carboethoxy  to  only  the  carbonyl-vinyl the  conjugation  conjugated  were  P2^2^2^  different  structure  carbonyl  II  conformation  by  conformation  form  group  32b).  represented  I,  of  by  almost  perfectly  Interestingly, central  double  the bond,  Of) C(12)-C(ll), of were  the  exist  dihedral  96.2  and  in  the  angles  176.5°  more  respectively.  differed  significantly  Instead  of  a l l  approximately  the  C(16)-0(4)-C(16)-C(17) the  two  possible  s-trans  conformation.  0(2)-C(13)-C(ll)-C(12)  groups  having  stable  the  heavy  same torsion  synclinal  The from  atoms plane,  (gauche)  the of  of  conformations the  were  forms.  ester  u  The  values  0(4)-C(16)-C(12)-C(ll)  conformation  the  angles  and  o  the  carboethoxy  present  substituent  in  form  lying  C(13)-0(2)-C(14)-C(15) rotated  +80°  and  -80°  to  I. in and  give  -78-  (b)  Figure  32.  Dibenzobarrelene Modifications.  Stereoviews Diester  of  the  21  in  Molecular (a)  the  Structures P2]/c  and  of  the  Diethyl  (b)  the  P2 2 2 1  1  1  The  Solid  State  Diester by  was  dissolving  ethanol 22  22  was  packed  molecular  Molecular  crystallized  this  added. in  compound  Large  the  of  22  double  (Figure  33).  The  differences  along  structures  are  enantiomers  in  Figure Diester  22  33.  two  alkyl  chiral,  a  a  were  amount  obtained  PI.  The  disymmetric  values groups  the  Di-n-Propyl  evaporation  small  torsion  three  the  most  also  carbon  crystals  solution  diethyl  found  display  22.  to  prepared  ether  to  contain  important  feature  diester of  the the  0(2)-C(13)-C(ll)-C(12)  and  and  defined  which  by  161.41°  6 . 5 1 °  significant  chains. are  a  conformation  angles, of  of  of  and  Diester  racemic  Although since  respectively conformational the  they  molecular  contain  both  amounts.  Stereoview  (Space  was  with  their  equal  in  of  slow  group  bond  0(A)-C(17)-C(12)-C(11)  by  prisms  space  structure  carbonyl-vinyl  Structure  Group  of PI).  the  Molecular  Structure  of  the  Di-n-propyl  -80-  The  Solid  The  State  diester  solutions prisms  to  homogeneous  this  23  which  with  those  Molecular  mp  material  determined  was  «=  as  was  145-6 The  from  was  f i r s t  ethanol  batch.  obtained  Structure  being  respectively  34a).  methine  (Figure  to  the  expected  hydrogen  and  from  by  slow  P2^2^2^ with  to  this  the  molecular  conformation  the  carbonyl  of  relationship oxygen  similar  the  torsion  in  of was  angles  and  63.7°  isopropyl  between  to  group  conformation  196.2°  observed  Large  apparently  space  bond  of  an  were The  carbonyl-double  synperiplanar  in  method  chloroform  solvent.  form  evaporation.  and  23.  concentrated  0(4)-C(15)-C(ll)-C(12) The  Diester  precipitating  observed  by  disymmetric and  conformed  as  Diisopropyl  the  obtained  ethanol  0(2)-C(13)-C(12)-C(ll)  as  were  crystals  identified  the  crystallized  added  °C  neat  of  group  the  isopropyl  other  isopropyl  o "l containing group  ester  the  compounds.  molecules  in  1  any  As  required  given  by  single  the  symmetry  crystal  are  of  this  present  in  space  only  one  chirality. A  larger  batch  in  specimen  order  confirmation  was  the  same  f u l l  structure  the  two  dimorphs  learned  to  found  attempted  how see  but  analysis  and  below),  successful  identical  explore  material  spectroscopic  cence,  to  with  its it  with was  were  in  dimorph  performed.  the  the  two  in  were  the  selected  we  space  though  were  not  group the  from  FTIR  solution  Pbca m a t e r i a l ,  and  was  which  group with  then  points solid  different.  state  same  dealing  Pbca  and  the  space  melting  significantly (solid  from  When a  crystallographic  materials  of  that  the  crystallization case  was  chemistry.  Even  their  properties  specific only  state  discovered  identical,  chemical identify  solid  was a  morphology  and  of state  Having lumines-  analyzed was  a  and  obtained  -81-  pure  from  mixtures since  cyclohexane of  the  crystals  two of  solution.  dimorphs.  the  Crystallization  Crystallization  P2^2^2^  material  from  from  were  other  the  solvents  gave  melt  was  gratifying  in  an  exclusive  obtained  manner. The of  the  molecular  structure  chiral  have  similar  group  of  equal  amounts.  The  the  modification  0(2)-C(13)-C(ll)-C(12) respectively.  of  and  isopropyl  space  dimorph  (Figure  was  34b).  0(4)-C(17)-C(12)-C(ll) groups  conformations.  non-chiral  Pbca  of  Since  groups  both  both the  quite  similar  The  torsion  were  228.5°  modifications Pbca  were  modification  enantiomers  of  23  is  are  to  that  angles and 3 6 . 1 ° found  part  to  of  the  present  in  -82-  Figure Diester  23  34. in  Stereoviews its  (a)  of  P2^2 2 1  1  the  Molecular  Structures  and  (b)  Modifications.  Pbca  of  the  Diisopropyl  -83-  Conformational  Polymorphism.  Conformational of  different  its  shape  angles,  and  is  significantly  as  of  by  a n g l e s . ^  that  for  state  even  lepidopterane  (Figure  for  organic  compounds  that  organic  tional  a l l  of  an  often  organic  measurable  to  be  i f  it  have  very  35.  The  Molecular  Structure  of  solid  lengths,  rigid  can  defined  Lepidopterane.  can  out  be in by  structures, geometrical be  modifications,  s t r i c t l y  by  bond  crystallizes pointed  differences  state  determined  significant  polymorphism.  Figure  is  existence  descriptors  been  polymorphic  the  bond  has  present  polymorphism can  compound  compound It  as  different  structural  structural  presenting  in  parameters:  appear may  Corradini  molecule  these  same  that  35),  by  molecular  the  compounds  Since  argued  same  modifications.  d i f f e r e n c e s . ^ a l l  three Very  different  defined  the  conformation  defined  solid  Bernstein*^ such  The  torsion  alternative  p o l y m o r p h i s m was  conformers  modifications.^3  c  as  expected it  can  be  conforma-  -84-  Conformational structures slightly  of  the  different  modification. The  This  existence  different  solid  o r\ forces.  space,  O  which  weak  known  conformational  of  different  modifications  First  J  to  to  forces  molecular  the  intermolecular  ents. ^8  the be  antiperiplanar of  the  a  one  forms  crystals  of  of  crystal two  the  P2^/c  isomorphism.°^  molecular  justified  balance  by  structures,  in  considering  intra-  and  or  vice  search  from are  This  the  X-ray  also  dimorph II  can  may  be  these  the  not  be  and  represent  that  intermolecu-  For  a  of  indicates  outweighed factors  can  by  that  that other  probably  of  where  21  in to  group  has  ester large  an  decrease  been  substitu-  of  a  of  exceptions  number  preference  energetic be  minima.  interesting  alkoxy  the  energy  carboethoxy  dimorph  number  a  may  energetic  energy  by  is the  analysis  significant  and  structures  it  primary  structural  the  structural  The  free  the  While  defined  accompanied  P2^/c  from  intramolecular  instance,  the  results  structures. the  occupied  energy  uniquely  conformation of  lowest  different  be  the  atoms.^  alternative  may  conformation  information  form  for  forces  structure  preferred  principle,  conformational  versa.  maximize  non-bonded  structurally  may  to  packing  the  potential  molecular  the  close  antiperiplanar  there  conformation.  case  energy  Suggested  compounds,  be  or  tendency  structure  than  crystal  the  the  related  increased  that  a  intermolecular  more  conformational  is  forces  in  to  can  from  between  Variations  shown  occur  there  closely  between  in  conformations,  the  Interestingly,  is  as  in  23.  phenomenon  according  several  presents  and  occur  the  notice  21  in  Et/Et-21  arrangement,  lead  diesters  evident  of  non-bonded  may  of  clearly  conformers  interatomic  balance  dimorphs  phenomena  attractive  have  is  oc '  u  two  state  crystallization  lar  polymorphism  factors.  attributed  of  to  this  of  the  In to  the the  -85-  additional  stabilization  a,^-unsaturated ester  group  the  the  the  to  the  in  since  vinyl  s-trans  carbonyl  dimorph this  II  would  substituent.  The  can  be  explained  from very  intra-intermolecular  energetic  balance.  Spectral  Differences  Between  the  clearly  how  the  Dimorphs  some  subtle  trans  ethyl  group  two  dimorphs  of  drastic  alternatives  Diesters  the  behavior  rather  of  the  disfavor  crystallization  illustrates  of  g r o u p . T h e  project  nicely  differences  conformation  should  21  structural  diester  from  C(16)=0(4)  C(12)  conformation  neighboring  diethyl  delicate  of  attached  antiperiplanar against  system  gained  in  Et/Et-21  a  and  iPr/iPr-23.  Diethyl 1)  Diester  Solid  state  The  solid  were  obtained  run  in  21. FTIR  spectra.  state in  infrared  KBr matrices  chloroform  for  relative  intensities  and  the  strongly  dependent  on  the  between of  the  number  molecules  ene-dioate  -j^g  p  r  bands  portion  have  0  been p  0  s  e  d  (Figure  of  36),  comparison  asymmetric  spectral  correlations t e m s . * ^ ! 87  per  of  spectra  of  the  No  effects  apparent  of  for  number  the  molecular  were  correlation  frequencies  since  of  solution  The  A qualitative  attempted  proposed  a  frequencies  assignable  unit.***' was  while  purposes.  absorption media.  the  study  was  of  the  bands,  found could  the  to be  the  enoate  structure  on  and the  be  found number  conjugated  structure-spectral  similar  21  spectrum  and of  compound  enone  data sys-  absorption  1  J  i  •00  I  i  I  1  1  1  1  !  1 |  |  2800  '  1  !—i '  1  1  1  1  |  i  1  i  i  i  2400  1  2000  1—i  1  1—^  1  1  1 — i — i — i — i — i  1800  1600  1  i  1  i  1.  1  1—i  1400 ,  i  i  i  i — i — i  1200  i  i — i — i — j 1000  |  i—I  J  |—i—t—T  800  Wavenumbers Figure P2,2 2 1  36.  ]  S o l i d State (top)  FTIR  and P2 . / c  Spectra of D i e s t e r E t / E t - 2 1 i n Modifications.  its  600  (cm"*)  -87-  frequency  of  conjugated  carbonyl  systems  are  included  in  the  following  l i s t .  a)  Conjugation  absorption b)  to  the  c)  e)  than  5.2  The Figure and  a  and  the  was  1704  absorption 1  stretching  coplanarity  of  the  conjugated  system  s-trans  conformations  will  absorb  at  lower  conformers.  of  the  olefinic  frequency  bond  than  the  s-trans  the  C=0  and  in  an  frequency  for  conjugation  isolated  between  (Ai7 <  60  conjugated  than  1  the  C=C b o n d .  the  cm" )  with  for  the  C=0 s-cis  1  between s-trans,  and between  system  of  characterized strong  cm"  1  two and  by  strong a  ene-dioate  at  1705,  a  dimorph  vinyl  the  cm" .  carbonyl  cm" ).  presented  solution  1630  s-cis  smaller  relatively  1727  at  the  with  absorption  70  the  conjugation.  systems  ene-dioate  hand  the  in  in  other  reduce  difference is  causes  frequencies.  lower  ratio  36,  that  bond  at  >  The  C=C  occurs  C=C b o n d s (Au  a  lower  absorption  group  The  f)  In  than  The  carbonyl  forms  of  Conjugated  d)  at  effects  effect  frequencies  and  appear  Steric  reduce  with  a  intensities  0.6  I,  very  and  as  carbonyl  system  is at  3.5  in  the  s-cis  shown  in  the  bottom  sharp  absorption  relatively  shoulder  C=C a b s o r p t i o n  carbonyl  at  1633  vinyl  characterized 1710,  cm" . 1  absorptions  weaker  and  a  band  at  very  a weak  greater  conformers.  spectrum  at  Dimorph  1716 II  at  strong vinyl  1639  of  cm* on  frequencies  absorption by  is  1  the of  cm" . 1  carbonyl absorption  -88-  The  spectrum  different expected  of  degrees to  be  of  the  above  spectral  the  two  carbonyl  in  presence  in  the  band  of  carbonyl  The  in  the  form  on  the  other  the  s-trans  would  The  the  of  two  two  AT" =  intensity  ratio  and  a  In  the  solution  relates  to  the  low  indicate  a  to  vinyl 65  agree  which  were  well  seem  spectrum  and  with  a l l  to  (not  of  (closer  the  well  carbonyl shown) of  to  apparent  agree  intensity  s-trans  The  frequencies  non-conjugated  preferential  the  absorption 1  absorption  of  frequencies.  cm" ),  a l l  view  groups  absorption  the  carbonyl,  conjugated  carbonyl  seemed  different of  in  absorption  hand,  position  conjugated  structure.  unexpected the to  dependent  on  systems  the can  infrared  differentiate considered  as  conjugational spectroscopic  appearance  validity  these  dimorphs  state  II,  of  surprising  groups  the  the  conformation  with  most vinyl  for  both  groups.  question applied  an  rather  conjugation  bands,  observation  which  was  carbonyl/vinyl  molecular  striking  I  expectations.  more  the  the  two  dimorph  presumably  increase  of  manifested  spectrum  the  dimorph  serious  properties  of  form  structure-spectral  data  and  suggests  the  operation  structure.  The  spectral  observed  peak  measurements  polymorphic a  spectrum  the  be  spectral  the  of  crystal  almost  of  can  materials. warning  of  measurements.  to  carbonyl  8  d  the  by  peak  be  of  and  compounds  a  procedure uniquely  of  valuable  should of  the  solid aid  also  assigning from  as  factors  between  value  as  into  correlations  specific  the  results  normal  calls  differences  proposed  Our  I  to be the  infrared  -89-  2)  21  Solid  State  CPMAS  The  solid  state  were  solid the  recorded state  In  indicating  an  II  up  carbons. only  NMR S p e c t r a .  CPMAS 45  16  of  carbons).  The  case  are  independent  non-equivalent well  resolved  carbonyl the  of  nature  11  information  based  resonances  There  the  chemical be  is  8  on  the  shifts  to  carbonyl  the  peaks,  the  CPMAS  carbons not  correlated  1  only  22  however,  8  in the  solid  solution  methylene, carbonyl  44  where  there  formally of  22  only  can  one  resolve  spread  over  a  as  to  the  state  and  this  structural  understood  possible  composed  peaks  assignments  dimorph  since  From  was  however,  in  bands  of  and  certainty the  both  peaks  seems  spectrum  three  of  8  (methyl,  8  diester  non-equivalent  C NMR s p e c t r u m  3  of  spectrum  to  enough  with  number  spectrum  into  differences  better  the  u n i t .  infrared  of  disymmetry  complicated  asymmetric  the  II  aromatic  more  the  and  shows  carbons  even  unfortunately shift  I  the  21  contrast,  expected,  (sometimes,  from  is  per  found,  directly  substituent ^  In  diester  various  I  contrast  b a n d was  of  from  tetrasubstituted  molecules  In  evident  similar  modification  ppm.  cannot  the  and  non-equivalent  of  the  signals.  absorption  four  range  of  carbon  of  dimorphs  corresponding  structurally  protonated of  bands  of  The m o l e c u l a r  was  symmetry.  V  assignment  groups  37).  spectrum  resolved  bridgehead,  two  the  C2  3  C NMR s p e c t r a  3  structures  average to  1  MHz ( F i g u r e  solution,  The  within  C  molecular  spectra.  contains  at  l i  can  properties be  proposed  s p e c t r a ) .  8  o  • ^  I a)  The  CPMAS  at  the  Chemistry Division  1  3  C NMR s p e c t r a of  were  kindly  recorded by  the  National  Research  Prof.  Council  J . in  Ripmeester Ottawa.  (a)  r 140  i  160 Figure P2^2^2^  37.  1  1  1  120  100  80  CPMAS  Modifications  1  3  (*  C NMR S p e c t r a =  Spinning  of  Side  1 60 Et/Et-21 Bands).  in  its  1  r  40  20  (a)  P2 /c x  and  P P M  (b)  -  -91-  Diisopropyl 1)  Solid  State  Even present as  Diester FTIR  though  as  those  band  to  observed  one  (Figure were  38).  in  Two  cm''-.  at  by  1713  in  both  stretching  and  completely  the  the  the  different  the  at  1387,  cm"  in  1  bands  are  There observed  the  1374  P2^2^2^  typically  is  again  spectral  cm'  no  for  obvious  features  of  infrared  the  of  the  at  composed  other  vinyl  case  dimorphs  Pbca  and  The  21.  (doublets  cm"  of  1  the  carbonyl at  1635  were  very  carbon-hydrogen been  found  symmetric  instance,  1459  1704  one  bands  The  for  similar compound  and  only  had  c  at  was  spectrum  the  hj. h  groups,  respectively  and in  be and  occurred  1387,  the  to  1374  asymmetric  groups).  correlation ene-dioate  w  compound.  absorption  in  of  form,  isopropyl  of  absorption  the  just  1724 The  23  were  diethyl  at  cm"-'-.  diester  spectra  the  bands  weak  of  modification  of  1636  was  dimorphs  diethyl  P2^2^2j^  isopropyl  the  modification observed  two  r e g i o n s , ^ . 87  the  in  1  hand,  was  two  of  0  the  stretching  some  frequency  for  two  dimorph  relatively  Such  C-H bending'-'-  and  other a  dimorphs.  the  the  absorption  however,  asymmetric 1458  carbonyl  cm"-'- a n d  bending  of  equivalent  the  of  dimorphs case  vinyl  on  Interestingly,  similar  the  strong  modification,  absorption  in  structures  differences,  from  system  accompanied  Pbca  molecular smaller  ene-dioate the  spectra.  the  relatively  different  23.  between  the  chromophore.  expected  and  Figure  38. S o l i d S t a t e F T I R s p e c t r a o f D i e s t e r 23 i n i t s (A)  and (B) Pbca M o d i f i c a t i o n s .  P2 2 2 1  1  1  2)  Solid  state  The  solid  compound  up  21.  to  17  39)  The  bands  resolution  was  and  vinyl  163.6),  bridgehead 19.1), in with  obvious the  in and  methine  same  correlation  determined  in  be  that  in  the  methyl  made  was  found  from  (23.1,  not  dimorph. for  between  the the  structures.  a  to  have  four A5=34  The  21.9,  observed  (6  20.8  signals  of  19  well  (24).  region  aromatic), Hz  and  coincidence  carbons sp^  165.8 68.7),  The  much  methyl  four  resolve  and  consisted  of  Excellent  carbonyl  dissymmetry.  and  spectra  (69.5  tetrasubstituted  resolved Pbca  the  non-equivalent  vinylic  diisopropyl  as  the  carbons  did  the  expected.  to  The' s p e c t r u m of  of  methine  molecular  the  (two  signals  X-ray  carbons  belonging  number  resolved  three can  a l l  observed  manner  modification  modification  same  Hz  dimorphs  isopropyl  dimorph.  carbons  A5=64 only  and  Pbca  the  well  signals  144.9),  other  was  chiral  substantial  the  the  were  the  51.7)  of  for  presented  previously  the  (152.7  resolution  dimorph  the  non-equivalent  of  to  in  two  24  increased  modification  the  from  bands  isopropyl  obtained  indicating  carbons  of  the  resolved  the  were  and  signals  six  spectra  of  (54.3  a l l  NMR s p e c t r a .  spectrum  spectrum  the  C  observed  probably  the  L i  state  (Figure  compound in  CPMAS  in  the  region  methyl chemical  An  where and  in  P2^2^2^ of  this  groups.  No  shifts  and  Figure (B)  P2 2 2 1  1  39.  1  CPMAS  1  3  C NMR S p e c t r a  Modifications  (*  -  of  iPr/iPr-23  Spinning  Side  in  Bands).  its  (A)  -95-  Differences  in  Reactivity  Differences rearrangement particularly 21  in  its  Single  in  were  in  noticed  had  unreactive  crystals  of  melting.  crystal  Specific valuable  r e a c t i o n . ing  in  l  their  ' ^  effects.  relative  matrices  for  The  as  In  of  starting a  conversion  an  the  the to  for  diester  The  the  after  different  the  quantitative  The  a  absorption  periods  for  a l l  photolysis  time  are  laser  at  the of  other  or  of  of  the  expense  been  solid  very state  c r y s t a l l i z -  sometimes  give  environmental  solid  relating  diesters  the by  only  or  23,  i n KBr  conditions  system 120  the of  seconds.  differences to  the  that  observing  ene-dioate 60  and to  dispersed  using  30,  21  similar  samples, due  of  the  a  determined  of  intensity  nitrogen  compound  were  laser  were  a l l .  sometimes  manner  samples  nitrogen  photolysis  in  compound  irradiations  can  A  of  measurement  dimorphs  measured  the  only  state  materials.  diethyl  control  reactive  solid  crystals  have  molecular  conversions  vinyl  after  given  of  the  sluggishly  Longer  that a  the  the  arrangements  the  were  where  nature  having  a  with  laser a  this  have  percent  materials  of  most  conversions  principles  Me/Me-18.  infrared  constant  increased  of  min with  15-25%.  of  of  the  20  of  crystalline  crystals  to  influence  quantum y i e l d s  the  conditions  effects  efficiency  reacted  extent in  of  up  under  of  and m o l e c u l a r  to  order  that  which  opportunity  packing  before.  consumption  Assuming  state  and photolyzed  described  was  some  for  resulted  efficiency  described  the  a  clues  reaction  to  establishing  different  important state  reacted  solid  in  case  conversion  compounds  reaction  between  photolyzed  2-4%  Dimorphs.  relative  modification  crystals  resulted  the  interesting  P2^2^2]^  Between  differences  in in  -96-  their the the  extinction larger  the the  extinction  the  relative amount  obtained  of  coefficients coefficient  reaction  efficiency  of  normalized  23  results  confirmed  its  Interestingly, for  the  found  presented state view  are  larger  have  Table lene  of  IV.  a  that  common  and  the  are  crystal  and  since  appear  similar  different  Reaction  the  conversion  values  given  kinetic  The  results  IV.  compound.  larger  the  product  fact  These  distinctively  efficiency  structures.  observed  differences The  results  that  analysis  solid  point  Space  of  Crystalline  Relative  Dibenzobarre-  Efficiency  18  PT  1.0  21  P2T/C  0.8  21  P2 2 2  23  Pbca  1  23  a)  group  Relative  P  conversion  2  1  1  2  1  values  5  0.1  1  1.0  2  1  constant  of  requirements.  Diesters. Compound  of  diisopropyl  Table a  ratio  diethyl  the  the  the  time.  in  the  demonstrate from  by  reactive  reaction  reveal  Efficiencies  low  indicated  molecular  they  sample,  is  of  higher  crystalline  more  that  The  3  a  presented  modification  perhaps  of  irradiation  to  in  yields.'-  At  samples  observation  21  substantially  Relative  two  differences  important  appear.  respect  P2^2^2^  compound  X-ray  also  with  i n i t i a l  the  reactions may  the the  their  after  Pbca m o d i f i c a t i o n  for  dimorphs in  formed  quantum  quantum y i e l d w i l l  were  reactivity  the  efficiency  compound  low  or  absolute  reaction  products  in  and  ° -  within  6  conversions  of  3--20%.  Several recorded cal  other  in  the  results  which  l  of  relevant  rare  to  but  view,  the  kinetics  been  crystals  have  been  polymorphs  a  ^  1  Cases  may  This  precisely  radical  pairs  McBride  and  The which 40). was  from  i f  two  in  fact the  and  to  one  the  of  have,  been  photochemi-  the  main  factors  of  modern  foundations  in the  be  solid  case  of  9  of  coupling the  has  reactions,  at  product least  Topochemical controlled  also  in  the of  a  in  different  state  determining or  from  of  manner,  polymorphic molecular  behavior  between  present  totally  point  and  structures  modifications  the  effects  relative  crystal  chemical  their  thermally  analysis  in  their  been  The  a  reactions  by  phenomena,  on  the  the  the  same  one  factors  reaction solid  observed  in  are  similar.  photochemically  generated  of  azobisisobutyronitrile  (77)  studied  77  was  products,  by  1  two  of  was  of  impeded  the  crystal  preferred It  be  the  the  dimorphs  here, 9  from  crystal  disproportionation. would  be  photochemical  investigations. ^ >91  influence  reaction  from  presented  mainly  well.  may  the  co-workers.  contrast,  products  was  unimolecular  cases  the  the  the the  solution  observed  on  occur  originate In  reactivity  polymorphism on  establishing  difference  which  solution, is  as  shown  where  reactivity,  the  of  The  depends  mechanism. state  l  in  measured  affected  a r r a n g e m e n t s .  of  acids  interesting  been  have  effect  polymorphism on  have  must  The  Cohen  encountered but  polymorphic-dependent  cinnamic  and  of  highly  subject  of  a  effect  is  the  Schmidt  topochemistry.  which  literature.  from  helped  The  examples  by  radical forms  products  proposed the  shown  an  were  that  in  extruded  to  give  four  fragments  A  and  B  indistinguishable shown the  to  solid  nitrogen  of  (Figure  reactivity  form  from  state  the  molecule  95%  radical formation and  by  -98-  disturbance groups were the  and  of  the  their  postulated  neighboring to  recombination  abstraction similarity 100%  cage  balanced  be  more  would  between effect  the  CN  X  those  lead  to  in  case  required  to  the  operate  in  both  the the  factors  crystal  n i t r i l e  motions  however,  required  alternative  was  also  for  hydrogen  products. shown  modifications.  Me  9  The  from  a  1  Me  CN—(• Me _ A  Me  the  disturbances,  of  for  between  disproportionation  controlling  Me CN  7-CN  N2  Me B  —  1  Disproportionation s o l i d state  Me Me Me CN | | CN + )=C-N Me Me Me Me CN M  40.  These  1  the  77  Figure  9  Me  N=N  M E  to  reaction  found  interactions  molecules.  serious  compared  that  dipolar  Solution  and  Solid  CH  Me  2  CN~^  E  +  H-J-CN  Me  State  Me  Photochemistry  of  Azabisisobutyro-  n i t r i l e .  Another  example  of  solid  substantial  reactivity  study  of  Norrish  (78)  studied  were  the  found  41).  In  cis  (-30%)  to  in form  solution and  in and  trans  II  between  reaction  laboratory. ^ 9  amounts in  photochemical  differences  type  this  state  one  (-70%)  that of  the  of 3  two  dimorphs,  this  time  comes  with  from  the  a-adamantyl-p-chloro-acetophenone  Cis  depended crystal  cyclobutanols  phenomena,  and on  trans the  cyclobutanol  reaction  forms  (P2^/n)  were  formed.  products  medium  large In  (Figure  amounts the  of  other  modification  (C2/c)  the  quantitative  amounts.  The  was  found  lattices.  to The  7-hydrogen required C2/c  to  geometries  abstraction form  the  the  unexpected  was in  the  of  the  aryl  not  present  solution  isomer  molecular  to  be  steric and in  media.  the the ^  very  between  would  hindrance bulky  found the in  generated similar,  product  P2^/n  was  geometry  1,4-biradicals  cyclobutanol  group  trans  difference  the  found  Substantial  edge-on  interaction  with  were  cis  stable  remarkable  correlate  modification.  between  more  would  the  from  two  crystal i n i t i a l  the  motions  prohibitive in  moiety.  modification  and  in  the  this  case  The  was  in  dimorphs  the  develop  adamantyl  form  two  however,  be  to  latter  obviously  a  ci ;  Figure  41.  acetophenone.  Solid  State  Photochemistry  of  a-Adamantyl-p-chloro-  -100-  Th e  effects  influences  of  the  configuration diesters  of  the in  amenable  to  presented  here,  reaction  pathways  2)  w i l l  w i l l a l l  this  give  give  state, ments  the  have  pathways reaction products  in  arising  Figure  of  enantiomeric  group.  42.  Since  to  reaction  formed  42).  to one  of  in  as  we the  model  these the  case  of  relative  the  symmetric  substrate  are  theoretically  pathways  media  since of  these  any  of  of  making  and  refers it  will  the  crystal  and  4)  to  be  influence  In  the  solid  environ-  the  reaction  give  be  no  four  the  the  and  crystal  reaction to  3  1  expected  them.  and  products  paths  is  conditions  alternative  see,  are  not  different  (paths  there  structures therefore  (i.e.  two  alternatives  stereoselective  will  and  other  formation  four  case  These  stereoselectivity  products,  the  or  four  disymmetric  the  constitution  measurable  by  molecular  be  to  dibenzosemibullvalene  while  Under  relate  The  Two o f  solution  the be  this  determination  the  be  equivalent.  from  In  antipode.  hand,  found  formed.  preferential  expected  in  imental  the  the  enantiomer  isotropic  longer  is  can  above  on  selectivity.  (Figure  other  been  no  of  opposite  favor  on  type  thesis  product  the  may  this  presented  lattices  products  however,  one  degenerate  that  crystal  of  studied  polymorphism  solid  preferentially pathways  unequal  amenable with  state  a  shown  formation to  chiral  experspace  -101-  Figure  42.  The  Dibenzobarrelene  Molecular  An point,  and  is  the  profound  and  Chirality  Reaction  Crystal  feature,  symmetry  of  common their  structural  require is  of  Symmetrically  Substituted  Chirality.  disymmetry of  Pathways  Diesters.  interesting  consequences  mirror  Four  the  a l l  solid  the  on  comment.^  non-identity  of  and  diesters  state  disymmetry  additional  relationship  to  studied  molecular chemical  up  to  this  structure.  The  reactivity  are  very  2  two  objects  is  a  that  property  are that  related can  be  by  a  common  to  QO molecules  and  crystals.  c  A crystal  is  said  to  be  chiral  i f  it  lacks  -102-  symmetry that  convert  require be  operations  constructed  chiral  in  Crystal  account to  for  1983.  9  that  natural are  general  characteristics: conformations  is  in  that,  a  >  9  molecular r e a c t i o n .  and ?  3  the  useful  racemic 9  the  most  of  a l l  in  in  c h i r a l i t y  the  a  small  is  solution one  lattice  or  not  ensemble  can three  always  also  to  their  in  the  It  has  form  sometimes  it  From  has  been  noticed  and  P2^,  and  determined  up  dominated  by  chiral  corresponding c h i r a l i t y  can  be  that  cannot  state.  adopt  the  separate  c h i r a l i t y  in  a  the  f i r s t  solid  chiral  an  and,  average  (2)  form This  considers  in  conformational  maintain  motions,  to  without  classified  phase  solution  solid  rare.  been  P2^2^2^  liquid  deformations, in  ^  crystal,  amount  molecules  while  9  a  structures  that  conformational minor  does  relatively  Crystal  compounds  state,  for  must  probably  solution.  solid  fast  planes  disymmetric,  can  found,  crystal is  only  in  a  compounds  however, with  periodic  molecules  commonly  flexible  crystal  object  glide  3  (1)  when  chiral  c h i r a l .  according  except  a  as  found  through  in  since  categorized  achiral  conformations  sometimes  The  ^  symmetry  molecules chiral  9  c h i r a l i t y  building  18%  categories  Crystal  of  are  be  antipode.  groups)  sources  can  and  molecular  percentage,  c h i r a l i t y  molecular  be  mirror  homochiral  (space  can  centers,  repeating  groups.  without  groups  that  molecular  any  and  space  ways  This  from  c h i r a l i t y  achiral  65  its  While  approximately  ^  comp6unds  into  organizing  chiral  space  molecules  two  by  possible  two  inversion  molecular  c h i r a l i t y  demonstrated that  object  crystals,  230  as  arrangement.  crystallize  the  an  permanent  dimensional  such  rigid  significant distinction  contributions state  of  chemical  i  diesters  21  and  23  clearly  f a l l  in  category  and  can  be  -103-  considered  to  resolution"  of  in 21  the and  undergo binaphthyl  racemic  (P2]/c  the  conformations  two that  (compound  21),  nucleation  occurs  in  only  one  two  possibility under  to  such  found  to  crystal  a a  give  that  was  the  the  rate  nucleation precipitated  a  <^  case  set  crystal rate the  Asymmetric produces  form  entire  in  modification in  of  in  chiral the  the  occur of  racemic  amounts  very  may  in  different  modifications.  entire  solution,  can  equal or  23),  the  here  modifications  one  present  (compound  differ  experimental  of  however,  can  growth  in  appear 21.  seemed  pure  in  energy^  crystallization  crystals  diester  that  be  equilibrium  usually  Sometimes,  with  occurs  sample,  If  which  crystallize  from  the  P2]^2^2^  one  with  or  and  Pbca  for  under  repeatedly  be  crystals  so of  the  large  the  of  melt  conditions  in  exists them  Diester  the  Fortunately to  of  the  there  2  conditions.  crystallization  specifically  either  (P2^2^2^)  chiral  "spontaneous  8  of  since  classic  the  to  chiral  the  Nucleation  observed  preferential  Absolute Asymmetric  which  in  forms  given  case of  one  to  Pincock.^°  w i l l  similar  the  first  analogous  nucleation  enantiomeric  respectively. similar  be  by and  enantiomers may  that  favored  Pbca)  If  c h i r a l i t y . ^ ° • ^  Since  be  and  than  dynamic  process studied  respectively.  23  crystals,  is  a  23  the  will  was  be  found  cyclohexane  was  modifications,  nucleation  are  so  similar  conditions  as  case  this  of  with  presumably  compound  respect f i r s t  to  seed  the  formed  sample.  Synthesis.'  synthesis optically  was  2  defined  active  by  Markwald^  substances  from  in  1904  as  symmetrically  "a  reaction  constituted  -104-  compounds the  with  the  exclusion  of  modified cal  by  such  in  converted  which by  in  the  line  synthetic the  are by  active  also,  1  with  A  0  display  <  1  0  in  and  their  for  the  the  0  The  1  of  1  0  a  chiral in  goals  of  to  of  energetically chiral  generated 0  0  ,  success,  1  0  of  substrate  in  such  are  is the  process  occurs  or  ^ >107  literature  0  Research  in  host  agents  because reaction  this  where  influence  ^  of  diastereomeric  reports  the  more  challenges  different,  physical  a  asymmetric  enantiomeric  1  that  syntheses  degenerate  0  is  molecules  manner  important  synthesis  1  was  amounts."  most  solvents,  with  synthesis  a  with  stereochemi-  enantioselective  through  3  other  of  asymmetric  the  but  definition  "Asymmetric  unit  influence.  number  this  include  since  one  materials  Later,  unequal  normally  1  active  ensemble  asymmetric  the  been  modest  an  doubt  c a t a l y s t s ,  1  of  as  area  optically resolved  molecules  such  in  1  0  5  and  circularly  6  circumstance  environment solid  c h i r a l i t y  or  state. ^ 9  can  intriguing  state  molecular  have  special  chiral  main  increasing  l i g h t .  very the  solid  0  very  polarized  from  an  products  r e a g e n t s ,  1  in  definition  disymmetric  brought  order  n  produced  the  rendered  the  i  0  unit  without  states  0  optically  processes."  into  are  time,  chemistry.  pathways  has  reactant  become  transition  nature,  achiral  Markwald's  has  1  of  diastereoselectivity:  products  with  synthesis  analytical  as  present  use  and M o s h e r  an  a  stereoisomeric  At  a l l  Morrison  aspects  reaction  intermediate  i f  these  exist  converts It  arise  molecular  possibility  reaction  c h i r a l i t y .  only  may  should  in of the  be  when  the  structure  compounds the  an  solid  are  noted  that  that  the  the  term  compounds in  solution  scenario  asymmetric c h i r a l i t y  originates  many  symmetric  state  absolute crystal  disymmetry  is  synthesis  set i f  a  into  permanent  absolute  asymmetric  -105-  synthesis  refers  more  optically  active  products  influence  than  y i e l d .  9  2  formation  materials  has  capabilities exploiting  without  to  one  of  products  years  became  an  N a t t a  induce the  1  0  by  processes man  in  of  any  can  generate  external  quantitative  field  making  crystalline of  use  on  1  1  through  chiral  enantiomeric  crystal  engineering.  1  1  2  a  brought  of  "^  for  known  orientation  between  of  approximately  the  The  cycloaddition  in  the  two  the  related  work  by  solid a  a  9  '  was  a  by  state  by  carried  out  not  by  chiral and  chiral  and to  by  1  0  state  translation  with  a a  the  axis,  inclusion Penzien  developments  p a r a l l e l  in  the of a  of  from  the  face-to-face  compounds molecules  inversion  the  feasible  center-to-center  two  0  at  examples  came  1  of  over  of  1  of  reaction  workers  elegant  Monoolefinic when  the  report  workers  overcome  include  was  crystals  development  most  of  bromination  these  rational  the  until  pioneering  photocycloaddition  bonds '  it  Schmidt  induction  problems  l  ^  [2+2]  which  A .  1 0  of  synthesis  remarkable  f i r s t  double  4.2  asymmetric  about  the  starting  possibility  crystalline  described  constituted  requirements  are  asymmetric  the  Following  of  achiral  demonstrations  polymerization,  results  some  of  fact.  use  from  Although  purpose  solid  well  The  1  years  models  dimerization  of  the  the  dramatic  Ostromisslensky,  the  Science  of  ten  arrangement  by  Subsequent  of  reaction  than  the  experimental  in  o l e f i n s .  about  most  enantiospecific  compounds  by  ago  9  substances  chemistry.  for  feasibility  Institute  active  the  c h i r a l i t y 80  Weizmann  this  these  imposition  of  state  p,p-dimethyl-chalcone.  less  that  optically  solid  and  demonstrated achiral  of  this  Farina  compounds  been  over  that  period  fact  formation  of  crystal  recognized  by  the  the  3  The  1960s  to  to  distance can  have  undergoing  center  or  a  -106-  mirror  plane.  allowed  in  products tional  a x i s .  found  chiral  1  of  to  1  2  the  crystals  achiral  compounds  gave  the  70%.  work  the  83  in  use  general  of  (S)-sec-butyl] This  to  give  has  been  t  i  o  n  i n i t i a l  of  the  topic reader  92,112b,c  area  is  be  and  80  the  element would  to  the  case  (Figure  P2^2^2^.  the  solutions  chiral  which  former  found  to  be  in  a  81  compound  with  and  products  selective  formed  were  photolysis  active of  give  in  43)  is  transla-  While  optically  solid  focussed  crystals 84,  in of  order  of  44.  an  detailed  compounds  analysis  referred  in  reaction  80  in  manner. enantiom-  active  with  a  as  a  crystal  could  be  designed  a p p r o a c h was  quite  in  review  several to  obtain  that  compounds  employed  material  used  order  model  diolefinic  strategy  crystals  subsequently  The  a  The  optically  ensure  products.  on  disubstituted  Figure the  to  achiral  active of  to  group  dilute  was  use  was  other  optically the  in  compound  crystals  compounds  perpendicular  generating  satisfyingly  structure  (R)-or  79  symmetry  mirror-symmetric cyclobutanes  photolyzing  chiral  on  space  of  f i r s t  a  this  based  which  the  1 1 2  plane found  expected  was  of  which  the  and  excess  group.  chiral  79  eric  the  the  the  olefinic  diarylbutadienes  compound dimer  with  was  preparing  mixed  included  mirror  by  The  Further  a  only  simple  possibility  effective of  and  situation  in  made  before,  having  This  a  respectively,  was  crystal,  crystallize  these  82  mentioned  necessarily  crystals  of  a  As  was  84-sBu  chiral template and  [R=  space from  photolyzed  successful  and  articles  to  additional  informa-  Figure Substituted  44. Vinyl  Asymmetric  Synthesis  Diacrylates.  by  Reaction  of  Unsymmetrically  -108-  Asymmetric  Four the  Synthesis  chiral  racemic  photolyzed (20°C).  only  the  in  rotation factor  glc  the  the  of  specific  of  samples  two.  approximately  The  nothing  to  1  when four  the  the  a  20  0.1 min  at  rotation  weight  of  The  varied  the  the  to  were be  crystal  this  in  were  a l l  the  activity  The  as  optical  much  as  calculated, constant  photoproduct  substantial  since  V). by  of  temperature  optical  (Table  rotations  of  solution  detected  revealed  found  crystal  ambient  was  products  was  one  M benzene  irradiations  specific  rotation  21.  random,  product  chiral  samples  glc.  at  analysis  crystal  specific  by  of  for  the  Diester  selected  ml  containing  from  determined  21  photolysis  chiral  a l l  calculated  conversion contribute  5%.  Diethyl  polarimetric  However, of  of  laser  same  the  of  and  nitrogen the  rotation  was  crystals  analysis,  case  of  Reaction  modification  Although by  sample  single  with  samples  by  55  and  amounts  compound  the  within  from  the  a  each  percent  of  unreacted  21  is  achiral  in  confirmed  the  solution.  The  low  previous was  also  amount  of  conversions  observation observed product  of  obtained  the  that  without  in  relatively longer  resulting  these low  reaction  photolysis in  experiments  efficiency  periods  significant  did  crystal  not  of  21.  It  increase  the  melting.  -109-  21  55  TABLE V. S o l i d S t a t e Induced O p t i c a l A c t i v i t y space  w (g)  0.1303  group  P2 2 2 1  1  a a  % conversion  D  1  i n C r y s t a l s o f 21 melting  [o]D  0.050  2 8  13. 6  no  0.9650  M  0.040  2 9  14. 3  no  0.0824  IT  0.036  3 2  13. 7  no  0.2024  tt  0.056  2 0  13. 8  no  0.0236  P2]/c  0.000  12  3  0. 0  no  _  0.000  96 0  0. 0  -  Solution  a) Reading u n c e r t a i n t y ± 0 . 0 0 2 °  The by  e n a n t i o m e r i c excess o f the d i b e n z o s e m i b u l l v a l e n e 5 5 was NMR c h i r a l  shift  reagent  studies.  1 1 3  A  sample  determined of  d i b e n z o s e m i b u l l v a l e n e 5 5 was f i r s t a n a l y z e d w i t h the c h i r a l s h i f t Eu(hfc)3  [3-(heptafluoropropyl  ( I I I ) ] i n order to analyze resolution.  The  the  non-equivalent  racemic reagent  hydroxymethylene)-d-camphorato)europium possibilities  of  suitable  enantiomeric  protons Ha, Hb, He and Hd  (two d i a s t e -  -110-  reotopic  pairs, in  Figure  substituents  presented  Eu(hfc)3.  overlapping  4.15  Two  ppm  possible pair: (IH),  (Ha  and  signals,  (+)-Ha, 4.5-4.3  Although chemical  (-)-Ha, and  shifted  optically  this  active  methylene  resolution i n i t i a l l y  and  groups  after  at  resolved  each  (+)-Hb,  etc.,  5.20  4.10 of  (-)-Hb,  the  and  six  out  as  an  (IH),  of  1  Hd) of  ester eq  of  and  the  at  eight  enantiomeric  5.05  (IH),  4.70  from  the  (IH). the or  resolved from  information,  material  at  (He  into  protons  of  addition  4.32  non-equivalent  assignment  with  the  multiplets  non-equivalence  possible  of  significant  Hb)  four  (4H)  45)  it  should  signals,  the was  shed  as  arising  enantiomeric presumed  some  light  resolution  that on  analysis  this  is  not  of  the  question.  Hb  the  Figure  45.  Diethyl  Dibenzosemibullvalene  A  single  nitrogen largest evidence  The  crystal  laser  for  possible of  Four  of  Non-Equivalent Protons  21  weighing  approximately conversion.  melting  and  Diester  the  three After  in  the  Methylene  Groups  of  55.  65.4 hours  mg at  was -10  photolysis  conversion  and  photolyzed °C i n the  order  crystal  specific  with to  get  the the  presented  rotations  were  -Ill-  determined  to  the  chiral  pure  racemate  be  13.2%  shift but  material  lower  of  experiment) two  signals  they  must  enantiomer The  and  a  at  5.50  5.30  and  be  assigned  from  to  two be  The studied  (e.e.)  Synthesis  a  the  specific  was  found  however,  could  specific  ization  be  optical  correspond the  optical be  to  1  ^  by  to  of low  from  rotation  This  of  of  that  from and  (+  similar  the  we  eq  protons  the  of  the  at  the  previous of  these  concluded  different  of  to  signals  intensity  10%)  two  to  a  that  enantiomers. of  the  same  an  corresponds excess  to  suggests  optical  purity  an that  of  80%  [a] max=18°. D  23.  crystals  described  for  relatively fairly  22% w i t h  f i r s t ,  by  signals  present  chiral  correspond  induced  to  enantiomeric  Diester  to  the  (similar  the  two  ca.  obtained.  follow  deliberately  these  the  2  two  1  1  signals  the  relative  to  to  the  with  identical.  in  consistent  the 4  conversions  rotation  that  be  rotation  from  of  from  non-equivalent  60%.  Reaction  varied  found  analyzed  resolution  However,  Since  ratio  of  similar  crystals  samples was  1  to  ppm.  belonging  induction  manner  to  as  ppm. a  presented  were  chemically  photolyzed  in  in  intensity  excess  asymmetric  be  expected  maximum o p t i c a l  Asymmetric  and  section  When  interference  around 4.5  methylene  relative  samples  sample  significant  (86.8%)  found  enantiomeric  this  the  would  the  a  was  Integration  1 0 . 8 ° respectively.  reagent with  starting end  and  The  The  apparent  f i r s t  two  spontaneously to  seeding  a of  second a  compound  compound  large  high. no  of  21.  23  As  was  before,  number  of  percent  conversion,  prejudice entries  in  obtained batch  solution  where of  samples  to  the  Table  VI  material, crystall-  diester  23.  -112-  TABLE V I . S o l i d S t a t e Induced O p t i c a l A c t i v i t y i n S i n g l e C r y s t a l s o f 23 w (g)  space group  0.0515  P2 2 2 1  0.0325  1  1  % conversion  0.0212  batch*  15 5  +25 6  1  1 8  27 7  1  -0 072  13 4  -25 3  2  +0. 102 -0. 016  »  [a]n  0.0229  »  -0 120  22 1  -23 7  2  0.0273  »  -0 107  17 6  -22 3  2  -0 222  9 4  -28 2  2  0.0842 0.0195  «  -0 066  18 2  -18 6  2  0.0318  »  -0 163  20 9  -24 5  2  0.0451  »  -0 212  22 2  -21 2  2  0 000  20 0  0 0  -  0 000  95 0  0 0  _  0.050  Pbca _  Solution *Batch deliberate  The  1 o b t a i n e d by spontaneous c r y s t a l l i z a t i o n .  (AAS)  by  seeding..  optical  yields  of  the c h i r a l d i i s o p r o p y l  p h o t o p r o d u c t 57 were i n v e s t i g a t e d diester  Batch 2 o b t a i n e d  55  dibenzosemibullvalene  i n a s i m i l a r manner as f o r  the  by c h i r a l s h i f t reagent a n a l y s i s . The e n a n t i o m e r i c  o f the two n o n - e q u i v a l e n t  i s o p r o p y l methine p r o t o n s ,  resolution  -CH( 0113)2,  o b t a i n e d a f t e r a d d i t i o n o f 1 eq o f E u ( h f c ) . From o r i g i n a l c h e m i c a l 3  a t S 5.20 and 5.00 (the  latter  H(C4b),  methine  the  isopropyl  signal  overlapping  multiplets  shifted  with  diethyl  a  A  S  shifts  singlet  and s p l i t  W  of  into four  s i g n a l s a t 6 5.73, 5.63, 5.20 and 5.08 ( F i g u r e 4 6 ) . In o r d e r t o e s t i m a t e the e n a n t i o m e r i c p u r i t y o f the  chiral  photopro-  -113-  ducts  the  samples.  chiral  shift  f i r s t  sample  The  conversion order  to  ([a]n  avoid  the  66%  be  could  The  alteration  Two  conditions Figure  46  solid  of  signals  clearly of  their  the  type  and  obtained  (2) over  for a  -  a  single  which  enantiomeric  content  during  sample of  was  obtained  single  two  different  photolyzed was  by  crystals  both  experiments  and  5.25)  had  they  synthesis  relatively  crystal  on  product  time large  were  presented  quantitative  (1)  f i r s t  performed  the  (e.e.>97%).  that  was  not  to  15%  separated  in  purification  p a r t i a l l y u n t i l  a  recrys-  purity  of  2 4 . 6 ° ) .  racemate  the  a  number  5.95  method in  a  in  indicates  the  the  -  D  (fi  state . asymmetric  reaction are  ([a]  obtained  where  limitations f i r s t  reached  from  second  from  analysis  from  to  The  products  spectra  other.  came  - 2 5 ° )  =  (recrystallization). t a l l i z i n g  reagent  consistent  clearly  four.  The  enantiomeric  The  results  represent through  a  of  spectrum excess  each  f i r s t  within  example  in the  are of  the a  photochemical  enantiomeric  experiments.  under  shown  here  unimolecular high  with  observed  presented  the  consistently number  were  1  1  5  yields  -114-  CH  I  3  —0—C—CH  'ii i  i  3  i i ' i i | i i i i i ' i i i i  5.0 ppm Optically Active  Figure Optically  The  46. Active  optical  asymmetric and  Partial  *H  (bottom)  Diester  yields  found  to  unimolecular  reactions  counterparts.  First,  specific finding in  a  a  reported  syntheses,  sometimes  NMR  a l l vary may  in  Spectra 57  for  after  a l l  zero  have  unimolecular  some  arrangements  suitable  crystal  bimolecular  reaction  involves  100%.  1 1 2  which  structure.  of  of  have  in  two  (top)  solid  been  suggest  that  bimolecular  the  require  chances  chemical  lattice  state  capricious  principle  each  and  Eu(hfc)3_  their  decrease  Second, of  eq  over  not may  disturbance  1  Qur r e s u l t s  advantages do  Racemic  examples  reactions,  reactions  intermolecular chiral  to  MHz) o f  Addition of  previous  bimolecular  from  (300  sites  of  event rather  -115-  than  one,  and  translates  into  Mechanistic  The 23,  this a  clearly  decrease  indicate  If  f i r s t , one  carbon  atom. of  modes,  of  the  assume  as  there  vinyl 1-4  and  indicates  that + 4 ) .  over  regarding versus  4)  path  there  is  These  are  a l l  and  four  are  solid 2  o t h e r .  do do  1  1  1  formation  nearby  aromatic  and  C(12) ,  the  isotropic from  one  case (1  that  of  2)  us  whether  (1  give  any  path  2,  the  diester  +  versus  two  bridging  in  fact  paths  t e l l  and  dibenzosemibullvalThe  0  they  path  bond  starting  one  in  not  Zimmerman  isoenergetic  to  and  crystalline  benzo-vinyl  state,  lead  the  C(ll)  possible  which  a  21  stereospecific  by  and  nor of  and  vinyl  however,  importance  of  involves  d i s c r i m i n a t i o n between  versa,  diesters  necessarily  and  give  from  proposed  sites,  which  Synthesis.  rearrangement  group  control  3  stereoselective  the 1  -  1  Asymmetric  enantioselectivity  results, vice  4  of  1  dimorphs,  reaction  In  total  or  the  paths  100%  relative  23  versus +  2)  is  information or  of  path  3  4.  It  is  possible  by  determining  correlating  with  ( 3 + 4 ) ,  the  42),  3  of  topochemical  mechanism  step  two  before.  paths  of  highly  there  enantiomer,  proceeds  favored  a  atoms  (Figure  sets  of  induction.  State  biradical  are  loss  di-7r-methane  is  re-system,  discussed  reaction  (3  Solid  both  the  the  Since  enantiomer,  paths  the  compounds  carbon  dibenzobarrelene ene  that  faster  asymmetric  with  the  paths  solution  in  a  product-determining  between  faces  we  to  of  obtained  dibenzobarrelene  the  lead  Implications  results  reaction.  may  i t  however the  with  to  differentiate  absolute the  between  configuration  absolute  of  the  configuration  paths  ( 1 + 2 )  starting of  the  and  material  (3  +  and  photoproduct.  -116-  S t u d i e s o f t h i s type were c a r r i e d  C o r r e l a t i o n o f the A b s o l u t e Diester  pro-(-)-23  Stereochemistry  (P2 2 2 1  out.  1  form)  1  and  o f the C r y s t a l l i n e D i i s o p r o p y l i t s O p t i c a l l y Pure  Photoproduct  57.  (-)-Dibenzosemibullvalene  A large single crystal  (55  mg)  of  pro-(-)-23  was  grown  by  slow  e v a p o r a t i o n from a seeded (batch 2) e t h a n o l s o l u t i o n . A s m a l l fragment c u t and X-ray anomalous d i s p e r s i o n a n a l y s i s was absolute  give  results tion  levorotatory  i n d i c a t e d that pro-(-)-23  designation  conferred 48a). the  to  IIP,  12M  the molecule  In t h i s approach one  o f the s i n g l e bond about angles  (  [a]  torsion  D  corresponds  focuses  on  p h o t o l y z e d and  the  confirmed  -25.4, CHCI3). The  =  to the  absolute  configuraformalism.  conformational  1 1 7  disymmetry (Figure  determines  between  which  the s m a l l e s t t o r s i o n angle  or f i d u c i a r y groups, a t t a c h e d to each the  conformation and  is  to  be  (counter-clockwise  0(4)-C(17)-C(12)-C(ll).  rotation)  is  end  specified:  (clockwise r o t a t i o n ) i s designated P (plus)  angle  X-ray  by the e s t e r groups a t C ( l l ) and C(12)  0(2)-C(13)-C(ll)-C(12)  p o s i t i v e t o r s i o n angle negative  to o b t a i n the  3  by the c o n f o r m a t i o n a l c h i r a l i t y  groups o f h i g h e s t p r i o r i t y ,  torsion  fragment was  photoproduct  d e s i g n a t e d as IIP, 12M  The  1  c o n f i g u r a t i o n o f d i e s t e r p r o - ( - ) - 2 3 by u s i n g oxygen as the heavy  atom. A t the same time the remaining to  performed ^  was  A  and  a  designated  M  (minus). In o r d e r to o b t a i n the (-)-57,  a  crystallization,  up  product  sample  absolute of  to 56% pure,  this  configuration m a t e r i a l was  of  the  levorotatory  i s o l a t e d by  and then f u r t h e r p u r i f i e d by  fractional  derivatizing  -117-  th e  remaining  starting  material  chromatographic s e p a r a t i o n . achieved  from  P432^2)  ethanol  suitable  analysis.  The  1 1 0  shown i n F i g u r e (due  to the  absolute (S)-ll  47,  for  to  give  X-ray  perfectly  (-)-57  pure  dispersion  configuration  following was  i n Figure  o f the  (S)-4b,  48c  easily  crystallographic  four c h i r a l centers,  (S)-8b,  can be  by  square c r y s t a l s (space group  anomalous  found to be  and  (S)-8c,  and  described  as:  (S)-9,  as  (S)-8d  d i f f e r e n t numbering used i n the c r y s t a l l o g r a p h i c a n a l y s i s  configuration  and  diazomethane  C r y s t a l l i z a t i o n of  absolute was  with  the  (S)-10,  (S)-12).  COOiPr i  iPrOOC  7  Figure  As  47.  Absolute Configuration  indicated  photoproduct  absolute  rearrangement  of  c o m b i n a t i o n o f the small  where  configuration  pro-(-)-23 two.  49,  are  proceeds  hand,  also  (-)-57.  drawings  either  of  given, via  I t i s i n t e r e s t i n g to n o t i c e  the  reactant  the path  and  di-rr-methane 1, p a t h 2 or a  that path  2,  with  a  m o l e c u l a r motions, would l e a d to a photoproduct  t h a t resembles the X-ray d e r i v e d  i n v o l v e s no the  Figure  amount o f atomic and  structure other  in  of D i e s t e r  assuming  the  s t r u c t u r e 57-1.  Path 2  on  the  l e a s t amount o f m o l e c u l a r motion, which  change i n the r e l a t i v e o r i e n t a t i o n o f the  r e a c t i o n , would l e a d to s t r u c t u r e  57-11.  e s t e r groups  during  -118-  Figure 23  in  the  Diester  48.  Stereo-diagrams  Pro-(-)  23,  and  with  Absolute  Enantiomorphic Phase  (c)  Diisopropyl  ,  (b)  Configuration of: Local  Lattice  Dibenzosemibullvalene  (a)  Diester  Environment  (-)-57.  of  -119-  57-11  conformational isomerization  Crystal  Conformation  57-1  Crystal Figure the  49.  Possible  Observed Absolute  It  is  attached  known  to  feature,  may  be  the  arguments.  preferred Paths  1  C(12)-C(10a)  ment  indicates  be  than  the  It  contact should  in  stereoelectronic  the  Diester  23  a  that  Account  It  seems  possible,  however,  only  involve  from  d <  considered  where  for  diester  the  that of  this  ester  ester  at  23  shown  pathway  C(ll)-C(9a)  lattice group  C ( l l ) . with  the  conformational  between local  This  supports  57-1,  view  the  is  groups  at  This the  environC(12)  aspect van  is can der  A.  that of  of  surrounding the  of  bridging  Inspection  surrounding  3.3  point  aryl-vinyl  space  48b  the  carbonyl  c o n f o r m a t i o n . 119  cis-bisected  structure  not  influence  of  molecular  space  at  conformation  X-ray  free  Figure  atoms be  is  respectively.  free  of  the  2.  2  preferred  rings  in  one  and  that  appreciated  Waals  only  pathway  and  larger  the  cyclopropane  of  Pathways  Configurations.  that  present  involvement  Reaction  Conformation  the  other two  factors, carbonyl  such  as  differences  groups,  may  also  in  the play  -120-  important this  roles  thesis  products tive  further  carbons.  on  The  The  we  found of  shall  the  see, of  to  be  effects  reaction  path  described of  takes  the  it  the  place  results  2  activity expected  or  on  the  " ^  the  that  in  Part  solid  at  the  of  III  state  two  reported  basis  of on  alterna-  there  crystal  will lattice  to  two  unless  of  chiral  one  of  influence  provides  the  means  formation  of  only  relevant  to  the  prebiotic  foreign  for  one  of  the  is  an  the  the  question  conditions.  two of  9 2  .112,120  phases  phases  Once  on  the  asymmetric  since  synthesis  activity  Before  realized  identify  the  a  was  method  resolution  of  the  as  with  preferential  mechanism  with  could  of that  preferential  have in  is  statistical  products  describing  it  Identification a  the  optical  principle  7  VI,  enantiomorphous  induces  enantiomeric  and  labeled  occur  9  Table  the  sign  In  w i l l  significant  of  were  influence  optical  and  possible  products.  possible how  two  in  planned  e n a n t i o m o r p h s . •  extremely  absolute  was  spontaneity  the  chiral two  reported  selectively  depending  enantiomorphous  a  of  the  enantiomorphous  to  was  modification.  analyze  confers  23.  experiment  prepare  crystals  two  crystal  the  crystallization such  the  The  9  this to  Diester  photolysis  pro-(+)-enantiomorphs  that  probabilities  6  way  of  diisopropyl  desirable  into  whose  because  chiral  was  9  2,  convenient  23  modifications. pro-(-)-,  a  Resolution  batch  seeded  the  diester  under  the  involvement  from  deliberately  established  any  we  Spontaneous  crystals  crystals  of  The work  exploring  because  As  the  reaction.  effects.  Studies  before  at  differ  support  steric  the  aimed  that  vinyl  were  is  in  is  highly  originated detail  the  -121-  studies the  performed  methods  used  to  detect  the  probable  to  identify  each  Differentiation  between  the  nature  crystal  of  this  modification  chiral  should  influence,  be  mentioned  briefly.  attempted  by  the  dimorphs  two  differences with  several  in  however, a  large  The  number  best  behavior  that  to  period Since  of  few  the  low  vessel absent only of  1)  a  nitrogen  very  intense  procedures,  temperatures,  in  the  about  by  liquid  crystals  twenty  and  red  laser  the  the  Pbca  per  crystal,  This  method,  batches.  the  unique  would  be  diester  were  over  the  a  thesis).  undesirable quickly  when  23  develops  contained  this  luminescence display  PART V o f be  can  was  of  that  crystals  this  analysis  c r y s t a l l i z a t i o n  (see  modification  subtle  infrared  91).  crystals  irradiation  even  state  modification  Chiral  Since  find  analyzing  from  irradiation  bath.  of  for  luminescence  the  identification  Solid  page  several  photoproduct  was  inappropriate  P2^2^2^  laser.  nitrogen  seconds  (see  23  to  of  (microscopic  attempted).  discovered  immersing  of  from  dimorphs  attempts  therefore  the  the  of  a  tool  of  accumulation  serious  unsuccessful  useful  was  Pbca  microscopic  a  method  of  and  not  obtained  seconds  into  and  and  1  however,  consuming  crystals  with  present  be  crystals  the  identification very  to  analytical  illuminated found  was,  time  of  Visual  morphology were  found  too  1  ambiguous  light  was  was  was  their  polarized  spectroscopy  methods.  P2 2 2^  under  performed  at  in  a  proper  luminescence  is  totally  and the  the  procedure  takes  identification  method  choice.  Enantiomorphism of  Chiral  Crystals  of  Diester  23  from  Ethanol  Solution.  -122-  A  sample  boiling slow  consisting  ethanol  evaporation.  belonging  to  the  then  photolyzed  were  measured  a  for  striking  The  and  the  to  ing  enantioselective  Table  w  VII.  (g)  0  0319  0  0265  0  the  chiral  The  it  for 23.  of  a  Single  dissolved  allowed  The  rotation  to  and  and  classified  as  chiral  crystals  of  photoproducts  the  in  material  c r y s t a l l i z i n g  chiral 9  Table  experiments  impurity  or  VII  were  seed  in  Batch  3.  Crystals  of  23  % conversion  from  [a]n  4  1  -29  0  3  »  -0  050  7  4  -25  5  3  0230  »  -0  038  6  7  -24  7  3  0  0327  »  -0  052  5  1  -31  2  3  0  0267  -0  027  3  1  -32  6  3  0  0292  »  -0  028  3  4  -28  2  3  0  0453  «  -0  095  8  3  -25  3  3  0  1255  «  -0  093  2  6  -28  5  3  0  0292  »  -0  066  10  4  -21  7  3  0  0230  -0  047  8  1  -25  2  3  *Batch  3 was  1  obtained  from  ethanol  solution  indicated in  the  primarily determin-  batch*  038  1  were  7  -0  1  in by  presented  Further  kept  crystallize  collected  specific  c r y s t a l l i z a t i o n .  of  was  was  were  results  diester  involvement  23  modifications.  and  group  P2 2 2  before  preference  Photolysis  space  diester  crystals  optical  of  directed such  or  calculated.  pro-(-)-enantiomorph  mg o f  minutes  largest  absolute  test  800  few  racemic  and  and  of  without  deliberately  seeding.  -123-  2)  Enantiomorphism of  Open  samples  necked, above  1  ml  their  suspected lowering  of  in  point  seeds. the  a l l  The  cases  optical Table  the  the  The  comparable  Table (g)  to  Diester  23  material  Grown  from  VIII.  and  these  the  Melt  an  allowed  in  turned  after  out 1  conversions  ml  to  were  absolute  Surprisingly,  the  magnitude  obtained  of  from  the  Chiral  group  clearly single  Crystals  no  % conversion  20°C  destroy  the  of  more  of  from [a]i  145°C.  than  was  The  the  for  optical  Melt  I  batch  -23.5  melt  I  0.1093  -0.221  9.6  -21.1  melt  I  0.0973  -0.160  7.0  -23.5  melt  I  0.1148  -0.171  6.3  -24.5  melt  I  0.1249  -0.196  6.5  -24.1  melt  I  1  1  1  the  purities  specimens.  Batch  and  rotations  8.5  P2 2 2  min  results  -0.245  0.1228  10  added,  preference of  by  polycrystalline  measured.  crystalline  23  kept  crystallize  CHCI3  indicated  of  long  point  be  of  an  experiments  to  in  and  to  melting  complete  photolyzed,  percent  attempt  the  placed  melted,  s t i l l  Photolysis  space  was  mg w e r e  oven,  was  below  obtained  were  in  liquid  sample  100  Kugelrohr min  whole  indicate  those  20  10°C  rotations  in  a  to  pro-(-)-enantiomorph.  w  of  approximately in  for  samples  VIII  encountered  of  viscous  temperature of  23  introduced  melting  appearance. their  diester  vials,  Crystallization  in  Crystals  Containers.  Six  and  Chiral  -124-  3)  Enantiomorphism In  Sealed  Container  The vials  starting  much out  in of  of the  nine  samples,  Table  w  (g)  0  0540  0  0614  0  described  melting.  material  rotation  as  the  of  Diester  The  was  products,  same  line  in  analysis  (2) of  performed and  to  in  our  Grown  presented  samples  were  s t i l l  pro-(-)  deduced  from  that  Photolysis  space  of  the  Chiral  group  repeated  from  the  by  sealing  enantiomorphous  the  usual  surprise,  those  of  was  the  as  IX.  23  Melt  In  a  (A).  experiment  before  Crystals  in  the  the  and  photoproduct,  of  23  % conversion  optical  sample  phase by  results  previous  the  Crystals  way,  the  of  observing  were  experiment.  Seven  purity  of  was  s t i l l  very  high.  from  Batch  Melt  II.  [O]D  batch  147  11  4  -23  9  melt  II  »  +0  153  11  1  +22  5  melt  II  0515  »  +0  171  14  6  +22  7  melt  II  0  0636  »  -0  159  11  0  -22  8  melt  II  0  0678  -0  215  14  4  -22  0  melt  II  0  1016  »  -0  210  9  6  -21  5  melt  II  0  0952  »  -0  236  12  7  -19  5  melt  II  0  1026  n  -0  176  8  6  -20  0  melt  II  0  0996  it  -0  189  9  6  -19  8  melt  II  1  1  1  the  obtained  -0  P2 2 2  the  the  -125-  4)  Enantiomorphism i n C r y s t a l s of D i e s t e r 23 Grown from the M e l t (B).  Sealed Container  The all  experiments  attempts  in a  performed  up to t h i s p o i n t were v e r y i n t r i g u i n g  since  to d e s t r o y the presumed seed were u n s u c c e s s f u l even under the  c a r e f u l c o n d i t i o n s employed. The  involvement  of  an  adventitious  chiral  i m p u r i t y seemed r a t h e r remote s i n c e the g l c p u r i t y o f the samples employed was  100%  under c o n d i t i o n s  (integrated they had time  as  glc  area  where  =  0.05)  impurities  of  l/2000th  would have been d e t e c t e d e a s i l y  (provided  s i m i l a r d e t e c t o r response 23).  of  and d i d not  In o r d e r to exclude c o m p l e t e l y  the  order  have  identical  retention  the p o s s i b i l i t y o f h a v i n g a  " r e s i s t a n t " seed accompanying a l l the samples a n a l y z e d so f a r , we the  following  experiment:  d i s s o l v e d i n cyclohexane modification. dimorphic  The  individual vials, The  first  previous  single  confirmed.  crystals  The  crystals  were  collected  were  s e a l e d , melted and then a l l o w e d t o  s i g n i f i c a n t o b s e r v a t i o n was  f o r the samples  to  tendency  form  supercooled  could  pricked with  rigorously  were  shown i n T a b l e  then X.  deposited  glassy  be  Pbca, their  again  material  stainless  in  instead  were  tendency of  unsuccessful.  steel  p h o t o l y z e d and a n a l y z e d as b e f o r e and  the  crystall-  induced however when the v i a l s were opened flame-cleaned  was  crystallize.  f o r f a s t c r y s t a l l i z a t i o n . Attempts t o induce  Crystallization  samples  and  a clearly distinctive  i z a t i o n by t o u c h i n g the v i a l s w i t h a p i e c e o f dry i c e  a  g o f d i e s t e r 23  i n order to o b t a i n c r y s t a l s o f the racemic,  largest  identity  a sample c o n s i s t i n g of 1.5  designed  needle.  the r e s u l t s  and The are  Table  w  X.  Photolysis  space  (g)  0.0636  of  Chiral  Crystals  group  P2 2 2  of  23  from  % conversion  Batch  Melt  [a]n  III.  batch*  +0.084  6.0  +22.0  melt  III  0.0781  +0.066  4.5  +18.8  melt  III  0.1704  +0.052  4.9  +18.2  melt  III  0.1004  -0.112  5.5  -20.3  melt  III  0.1242  -0.173  6.0  -10.6  melt  III  0.1047  -0.119  4.7  -24.2  melt  III  0.1027  +0.124  6.8  +17.8  melt  III  0.0996  -0.105  4.1  -24.2  melt  III  1  Inspection  1  of  1  the  results  distribution  of  both  modification.  The  magnitude  s t i l l  suggests  samples.  The  a  interpreted  step  in  the  i n i t i a l  the  normal  final  high  of  to  of  to  indicate the  of  process.  that  the this  gives  phases  purity and  While was  of  the  of  of  the  most  of  a  random  the  P2^2^2^  photoproducts the  crystalline  high  enantiomeric  being  the  the  rate  methodology  planned  phenomenon  of  crystals  for  possibilities  pro-(-)-enantiomorph.  evidence  rotation  nucleation  experiments  reduce  X  specific  crystallize  indicative  crystallization  procedures  the  enantiomeric  crystallization  results  persistence  as  Table  enantiomorphous  reluctance  are  the  very  in  and  of  may  determining employed  executed  self-seeding, be  Self-seeding  responsible is  a  purity  by 1  2  using 1  for  concept  in  o  u  r  the that  -127-  i m p l i e s r e s i d u a l seeds as the d e t e r m i n i n g f a c t o r f o r a preponderance o f given  solid  phase.  This  phenomenon  H a v i n g a ^ w h i l e e x p e r i m e n t i n g on allyl-anilinium  Figure  equivalent  been  1 2 2  observed  spontaneous  and  documented  resolution  of  by  ethyl-  iodide (85).  o f E t h y l - a l l y l - a n i l i n i u m Iodide.  o f the q u a t e r n a r y s a l t grown from c h l o r o f o r m  of solvent  hemihedral group.  the  50. Spontaneous R e s o l u t i o n  Crystals  was  a  faces  of  because  crystallization) the  sample  had  been  crystallizes  ( c o n t a i n i n g one  shown in  a  to  present  chiral  space  -phe r e l a t i o n between hemihedral phases and o p t i c a l a c t i v i t y  e s t a b l i s h e d many y e a r s b e f o r e  the sodium ammonium t a r t r a t e s a l t .  had  by Pasteur i n h i s c l a s s i c a l s t u d i e s on 1 2 3  I t was a l s o  shown  that  85  slowly  r a c e m i z e s i n the same s o l v e n t b u t remains s t a b i l i z e d i n e t h a n o l . The  quaternary  s a l t 85 resembles d i e s t e r s E t / E t - 2 1 and i P r / i P r - 2 3 i n  t h a t they a l l e x i s t i n s o l u t i o n as an e q u i l i b r i u m o f enantiomers  and  in  that  a l l can  also c r y s t a l l i z e  two  interconverting  i n optically  active  -128-  modifications.  Havinga  observed t h a t i n twelve out  i z a t i o n experiments where c h l o r o f o r m filtered,  s e a l e d and  m a t e r i a l obtained our  results,  From  gave d e x t r o r o t a t o r y  when 85  glass-filtering, tion.  heated to d e s t r o y  was  solutions  85  of  adventitious ethanol  of fourteen had  been  seeds, the  solutions.  9 7  A l s o s i m i l a r to  h i g h l y r e l u c t a n t to undergo  seven experiments the m a t e r i a l s dextrorotatory),  one  obtained  additional  crystalliza-  were: t h r e e  one  ambiguous (probably  two  l e v o r o t a t o r y . Havinga i n t e r p r e t e d h i s r e s u l t s as an  paper-  crystalline  more c a r e f u l l y t r e a t e d , t h i s time by  the m a t e r i a l was  crystall-  racemic,  certainly dextrorotatory i n d i c a t i o n of  and true  spontaneous r e s o l u t i o n , t h a t i s , an event where the enantiomorphous phases can  appear  impurity.  without  any  chiral  Other o b s e r v a t i o n s  time i n the  scarce  influence,  either  a seed or a s t r a n g e  of s e l f - s e e d i n g have appeared  l i t e r a t u r e of t h i s  topic. 1 1 2  from  time  to  -129-  PART THE  I I I .  T H E REGIOSELECTIVITY  SOLID  39  Studied  and  compounds  shown  REARRANGEMENT  IN  STATE.  Compounds  The  OF T H E DI-TT-METHANE  in  Figure  Identification  studied  51  in  this  of  Photoproduct  section  are  Stereochemistry.  the  mixed  diesters  28  to  below.  COOR 2  Compound  the  R  Methyl  29  Methyl  1-Propyl  (nPr)  30  Methyl  2-Propyl  (iPr)  31  Methyl  2-Butyl  32  Methyl  1,1-Dimethyl-l-ethyl  33  Methyl  1-Pentyl  34  Methyl  2-Methyl-1-Butyl  35  Methyl  2,2-Dimethyl-l-propyl  36  Methyl  Menthyl  37  Methyl  Phenyl  38  Ethyl  39  Ethyl  51.  Mixed  Di-7r-Methane  (Me)  2  28  Figure  of  R^  Ethyl  (Et)  Diesters  (Et)  (sBu)  (nPen)  Rearrangement.  the  (neoPen)  (Ph)  2-Propyl  in  (iPen)  (Menth)  2-Butyl  Used  (tBu)  Study  (iPr) (sBu)  of  the  Regioselectivity  -130-  Compounds where  one  of  increasing 39  the  other  an  methyl  and/or  28 and  from  but  the  or  a  39  materials  as  products  were  in  clearly  the  t r i p l e t  Common this  series  singlets  to  the  was  a  at  attributed  to  from  each  were  assigned  z i l i c Other  state  hydrogens signals  in 37)  portion  duplicate  (a  set  of  intensity  of  signals and  ^'  1  4  two  to  were the  T  n  from  peaks,  and  each  resolution.  r  s  t  (glc-mass  the  and  regioisomer)  starting The  B,  mixtures  two of  expected  studied  and  group  two  of  signals  resolved  alkyl which and  was eight  in  and  pairs, bisben-  (Figure (or  were with  in  sharp  protons,  respectively  substituents  two  properties  cyclopropylic  the  of  18) .  sometimes  to  the  substituents  with  aromatic  C(4b)  and  photolysis  the  -7.5-7.0  f i  e  and  the  evidence  A  reaction 6  38  benzene,  rearrangement.  (Figure  attributed  ester  glc  isomeric  at  of  in  NMR s p e c t r a l  tertiary  C(8d)  ethyl  analysis  the  18  respectively.  structures  2  an  spectral  non-equivalent  corresponding  of  D  by  to  were  pattern  ppm.  compounds  according  the  a l l  In  expected,  and  reaction  of  other  spectra  was  diester  substituent  i n i t i a l l y  molecular  have  peak  -5.0  attached the  a  regioisomers,  The  case  relative  to  overlapping  the  of  di-rr-methane  and  regioisomer. to  case  complicated  the  Mass  one  groups  it  varied  products  NMR s p e c t r a  -4.5  ester  of  alkyl  group.  spectral  used.  an  exchanged,  As  that  found  by  phenyl  were  gave  the  derivatives  photolyzed  the  dibenzosemibullvalene  from  a  solutions.  that  required  or  were  of  exchanged  sec-butyl  solvent  indicated  series  was  groups  quantities  spectra)  the  ester  compound  in  with  groups  acetone  each  a  branching  to  photoproducts  the  comprise  isopropyl  acetonitrile  not  37  methyl  Compounds  mixture  to  the  size  two  for  28  aryl present  52). in in  variable  -131-  COOR2  COORl  COOR2  COORl  8d  8b  8b  8d  B  Figure  52.  Products  Dibenzobarrelene  It  has  sometimes dures .^  '  products  and  analysis  The  methyl  compounds  28  found  to  be  from  to  of  37 and the  useful  several  Rearrangement  by  relative  of  have  been  in  Mixed  in  this  from  the  of  the  purposes. diesters  context.  can  normally  reaction  be  reactions  stereochemistry  spectra  to  The  of  the  procethe  inferred  39  products  suited  methylene and  may  of  be  the  m i x t u r e s > , 1 2 5  ideally  38  that  chromatographic  however,  the  found  identification products  of  yields,  reports  di-w-methane  conventional  NMR s p e c t r a resonances  literature  related  determination  the  ester  quantification substituents  ^he  their of  Di-?r-Methane  in  inseparable  . 125  from  shown  products  be  the  Diesters  been,  stereoisomeric  from  from  have  from  for  easy  the  ethyl  also  been  -132-  The  spectrum  well  resolved  and  4.32)  groups  attached is  3.85 The  ppm)  to  of  same  the  were  XI  at  Table Mixtures  XI. of  Glc  C(8c)  with  having  of the  to  C(8b),  two  from  6  4  more  -  1  2  4  (Table  (ethyl) from  at  esters This  alkyl  group  position.  signals  the  glc  photolyses  were  analysis  are  shown  and  'H  NMR  Results  Dibenzobarrelene  From  Minor elc  r.t.  of  Photolysis  Diesters.  Product  Area%  S o l u t i on  X  Area%  H NMR 6  Product  (COTCH-J)  c  Area %  r . t.  Area%  3 . 70  52  15.30  u  3.86  48  15,.15  **  29  b  3 . 70  55  16.21  57  3.86  45  16, .00  43  10.80  45  30  b  3..70  55  55  3.86  45  10,.27  31  c  3..70  64  22.8/23.2*  60  3.85  36  21.,25  40  32  a'  3..70  61  16.23  60  3.86  39  15. .58  40  33  d  3..70  50  9.10  51  3.86  50  8, , 8 5  49  34  a'  3,.70  50  19.64  49  3.84  51  19,.26  51  35  d  3.,70  61  6.65  57  3.85  39  6. ,06  43  36  e  3..71  55  10.14  54  3.86  45  8. . 8 0  46  37  a  3.. 8 0  30  13.85  **  3.91  70  13,.85  **  38  a'  4. . 20*  53  12.47  52  4.35  47  12. .10  48  39  g  4. .20*  50  20.7/21.1*  49  4.35  50  19, .88  51  Conditions 10;  270,  10.  a')  195,  [Oven 15;  *  Two d i a s t e r e o m e r s  *  The Not  signals enough  of  the  in  56).  a  Glc  and 4.15  XI).  benzylic  areas  sharp  (ethyl)  deshielded  the  solution  two  quartets  methyl  methyl  integrated  results  the  C ( 8 b ) the  to  the  showed  (methylene  and  attached  (COoCH^  6  3.85  clearly  28  195,  **  and  to  with  (the  Mai or  Glct  •f  well  mixture  respectively  intensities  "Mixed"  H NMR  3.70  6  ester  Figure  Compound X  at  assigned  the  mixtures in  product  consistent  correlate  and  each  respectively  integrated  found  Table  singlets  that  assignment (i.e.  of  temperature b)  200,  15;  formed,  see  ethyl  ester  resolution  ( ° C ) , column head c)  PART  obtained  195,  10;  pressure  220,  15;  used  for  e)  (psi)]: 245,  15;  IV.  methylenes on  d)  glc.  were  integration.  a) g)  That  the  spectral  be  demonstrated  the  diester  structure obtained  in  assignment  the  Me/iPr-30.  of  each  after  fractional  of  they  case  of  The  these  two  had been  independently  in  are  the  thesis  shown  in  (Figure Figure  53).  photoproducts  compounds  63A  separated  a  The  and  spectrum  regioisomeric  p y l -11 - m e t h y l - d i b e n z o b a r r e l e n e of  the  NMR  recrystallization  synthesized  of  by  44  correct  the  the  lengthy  The  diester  manner  which  NMR s p e c t r a  products X-ray  is  of  from  and  discussed  compounds  iPrOOC  hv  44  acetone  63A (Only  Figure  53.  Independent  Synthesis  of  low  the  Product)  Photoproduct  63A.  from  crystal  63A  54.  iPrOOC  could  dibenzosemibullvalenes  stereospecific diester  63B,  and  a  procedure.  was  were yield  was  also  10-isoproin  63A  Part and  VI 63B  -134-  300  MHz  COOi Pr COOMe  63A  TMS  . U L . 1 r-t  1 I N ' I |  i i j I I I r 1  r COOMe COOi Pr  H 0 2  J L _I i I I I | i I I i | i I I I LJI | i ' I i T i i i i -|-n i-i-r r-ri-i-| TI I T 3  Figure  54.  NMR  Spectra  2  o f D i b e n z o s e m i b u l l v a l e n e s 63A  1  0  PPM  ( t o p ) and 63B  (bottom).  Another throughout measured  consistent  and  probably  the mixed d i e s t e r s e r i e s was on  a  DB-1  c a p i l l a r y column.  structure-diagnostic  feature  found on the g l c r e t e n t i o n times The t r e n d was c h a r a c t e r i z e d by  -135-  shorter  retention  photoproducts times and  than  the  and  the  times by  the  isomers  integrated  area  for fact  the that  B.  The  of  their  starting the  A  isomers  retention glc  materials had  times  of  are  also  peaks  compared  longer  each  to  the  retention  solution  presented  product  in  Table  XI. Once was  the  found  structural  that  the  spectrometric could  be  fragmentation  measurements  correlated  regiochemistry.  The  characterized  the  molecular is  that  ester of  the  on  two  +  Ester  undergo  the  indicated  loss  of  a  more  70eV  fragments  with  Table  at  C(8b)  key  in  the  manner  at  C(8c)  are  lost  at  C(8b)  bearing  impact  ionization  high  mass  range  was  either  as  mass  spectral  on  the  location  positions  behavior of  and  the  consists  55):  lost  to  glc-mass  the  Figure  be  it  dibenzosemibullvalene  cyclopropyl  can  the  substituents,  to  and  determined  from  the  depends  XII  been  electron  ester  The  had  obtained  pattern two  consistent  substituents  p a r t i a l l y  give  [M -  mainly  as  to  (ROH + [M -  give  C0)] . +  R - 0  ,  ]  +  or  as  C0)] . +  substituents normal  McLafferty  in  (1)  above.  substituents  at  C(8c)  available.  by  peaks  with  non-equivalent  (compare  in  the  fragments.  these  glc  patterns  obtained  of  substituents  or  the  fragmentation  radical  the  of  successfully  nature  Ester  (R-0(3)  as  Ester +  -  by  following  -R-OH] , (2)  [M  the  group  (1) [M  or  identity  This even  rearrangement  fragmentation i f  abstractable  hydrogens  besides  7-hydrogens  the  can  fragmentation  pathway  is  not  shared  by  suitable  for  abstraction  are  -136-  It with any  has the  other  atom the  been  proposed  aid  of  alcohol  t r a n s f e r . presence  hydrogen loss  of  1  of  2  second  from  a  1)  the  the  ester  2  required group  abstraction protonated  group  losing the  on  the  or  should  in  the  would  involved case  oxygen  in  and,  fragment hydrogen hydrogen  3)  ester  as the  a  transfer  between  oxygen  close  to  at  the  C(8c), alkoxy  suggested  to at  reactive  hydrogen,  may  transfer  in  other  be  involved  C(4b). also  The  explain  direction  group  in  in this  2)  oxygen should Figure process  involvement why  [from  there  ester  at  of  is  lost  this,  C(8b)  transfer,  two  functional  of  this  it  type  photoproducts  ester as  a  should  that  at  the  bisbenzylic  presumably  ester  the  molecular  seems  the  by  group  significant to  and  esters  hydrogen  the  is  no  3)  abstracted  55,  on:  hydrogen  double  same  be  a  (uncatalyzed)  the  of  of  abstractor  and,  f i r s t  The  based  esters,  the  the  etc.).  is  A mechanism  be  f i r s t  aid  undergo for  is  "intramolecular  dibenzosemibullvalene  55).  As  in  between  atom  the  the  proton  2)  required  hydrogen  proton  f i r s t  proximity  molecule  carbonyls,  as  or  hydrogen  make  mechanism  rearrangement.  group  to  often  methanol  alcohol  to  not  of  double  unimportant,  do  geometry  a  the  is  oxygen  a  compound w i t h  fragment,  alkoxy  attached  the  double  protonated  likely  able  evidence,  loss  an  amines,  ester  regioisomeric  the  group  of  the  double  of  loss  referred  a  1)  (Figure most  the  the  the from  been  The  0  that:  transferred  C(8b),  2  arises  ethers,  alcohol  permit  the  require  carbonyl be  of  1  that  has  carbonyl  s h i f t s .  groups  the  ^  an  alkoxy  1,3-hydrogen catalysis,  for  1 2  from  stereochemistry  by  for  functional  molecule  stereochemical  esters  (alcohols,  Evidence  0  of  compounds,  carboxylic  second  functional 1  basis  A requirement  0  alcohol  c a t a l y s i s . "  the  deuterated  abstraction an  on  at  more  hydrogen C(8c)].  -137-  The  loss  of  the  [R-OH  + CO] fragments t h a t account f o r peaks o f  c o n s i s t e n t l y l a r g e i n t e n s i t y , may occur v i a two c o n s e c u t i v e is  possible  that  the  second step may,  i n some cases,  be s u f f i c i e n t l y  f o r the o b s e r v a t i o n  reasonable  t h i s type o f f r a g m e n t a t i o n a t the C ( 8 b ) e s t e r group i s  r e a l i z e d by i n i t i a l McLafferty initial  is  probably  the  seems  competing  f r a g m e n t a t i o n o c c u r r i n g by  charge l o c a l i z a t i o n a t t h a t p o s i t i o n .  transfer,  with  the  the  ester  first  group  f a s h i o n t o y i e l d abundant M  +  McLafferty  at  rearrangement  hydrogen  at  to  the  other  abstraction  - ROthe  and M  +  subsequent  ester  (hydrogen  - (RO- + CO) i o n s . The l a c k o f group  at  C ( 8 c ) i s somewhat  a relatively  abstraction  slower  process  [ H ( 4 b ) ] and a - c l e a v a g e )  a l t e r n a t i v e s . A l t h o u g h a d e t a i l e d machanism s h o u l d isotopically  and  C ( 8 c ) fragments i n a normal a-cleavage  i n t r i g u i n g and p r o b a b l y r e s u l t s from b e i n g  with  ion. It  charge l o c a l i z a t i o n a t C ( 8 c ) b u t t h a t the  rearrangement  Competing  compared  R-OH  It  f a s t not to allow that  o f the M* -  steps.  necessitate  studies  l a b e l e d compounds, the s t r u c t u r e - d i a g n o s t i c v a l u e o f  the mass s p e c t r a o f these compounds seems almost u n d e n i a b l e .  -138-  Figure  55.  Stereospecific Electron  Dibenzosemibullvalene  Diesters.  Impact  Induced  Fragmentation  of  -139-  Table  XII.  High  Mass  Fragmentation  of  the  Dibenzosemibullvalene  Diesters.  COORi COOR2  4  5  Compound R  L  Alkyl R  63A  iPr  Me  64A  sBu  Me  65A  tBu  Me  66A  nPen  Me  67A  iPen  Me  68A  neoPen  Me  2  R-OH  iPr(5)  tBu(5)  iPen(3)  group  lost  as  (rel.  CO  intensity):  R-0-  ROH +  RO• +  CO  McLafferty  -  iPr(65)  Me(10)  iPr(30)  -  sBu(94)  -  sBu(58)  -  tBu(96)  -  tBu(lOO)  -  Pen(30)  Me(3)  -  iPen(60)  Me(5)  iPen(20)  neoPen(lO)  -  neoPen(lO)  sBu(lOO)  -  sBu(ll)  -  -  72A  Sbu  Et  sBu(15)  63B  Me  iPr  Me(15)  iPr(10)  Me(20)  iPr(lOO)  -  64B  Me  sBu  Me(9)  sBu(ll)  Me(8)  sBu(lOO)  -  65B  Me  tBu  -  tBu(ll)  -  tBu(100)  tBu(6)  66B  Me  nPen  -  nPen(25  Me(20)  nPen(lOO)  -  67B  Me  iPen  -  -  iPen(25)  68B  Me  neoPen  -  -  neoPen(25)  72B  Et  sBu  EtCll)  sBuC8")  Et(80)  iPen(5)  -  neoPen(5)  -  sBu(lOO)  -  -140-  Photolysis  With  of  Mixed  only  Me/Menth-36, in  compounds  were  ratios  two  we  described  Diesters  this  that  therefore in  the  from  sample  reducing  the  out  crystals  on  was  independent  to  -25%  became  of  results  The  are  the also  f i r s t  that  the  solid  state  in  as  low  as  was  (after  of  the  on  is  shown  comparative  observation  one  can  selectivity  in  to  solution  diester  be  contrast,  small  media  a  general from  and u n p r e d i c t a b l e  Figure  the  product The  reproducible crystals  studies the  or  that  by  carried  product  which  ratio  led  the  to  up  crystals  regioselectivity  56, w h e r e  to  to  in  profoundly  solution  The  moderate  These  the  be  the  graph  variations  tends  manner.  the  more  The  trend.  studies  the  solution  purposes.  from be  structure.  these  ranges  draw can  when  in  that  and  photolyses.  irradiations  results  the  and  Detailed  consumption  in  for  to  powdering  in  Me/nPent-33  solution  indicated  State.  temperatures.  state  found  -50°C.  conversion  state  prepared  the  by  Solid  compounds  solid  in  affected  the  ambient  the  for  than  discontinuous  in  solids  material  solid  regioselectivity  state,  as  A summary  product  seems  to  by  at  included  dibenzobarrelene  what  not  percent  starting  in  solids  manner  the  in  diesters  compound M e / i P r - 3 0  the  unreactive).  obtained  the  of  were  in  and  temperature of  mixed  same  and  presented  photolyzed  observed  to  the  section  regioselectivity sample  Solution  exceptions,  found  determined  in  be  are  Figure  56  is  affected  in  the  to  the  introduced  results  moderate  and  regioselectivity large  and  indicate  seems  to  that follow  in  the  to  vary  solid in  a  -141-  SOLUTION  SOLID  R =  Et  nPr  iPr  sBu  tBu  iPen neoPen  Ph  iPr*  sBu* "Ethyl  COMPOUND:  28  Figure lectivity  29  56. of  30  31  32  34  Comparison Between  Compounds  28  to  39.  35 the  37  Solution  STATE  38  39  and  Solid  m  e  t h y l  State  instead groups Regiose-  o  -142-  Analysis  of  Given  the  the  substituents that from  the  steric  A  in  factors.  carbonyl  It product  Steric  1  2  8  the  one  by  of  g r o u p s  ^  1  the  (  ^  state  to  of  effect  of  crowding  the  can  operate  a  by  that  resonance  with  to  of  mainly  inducing  is  by  a  of  steric  a  primary  properties  secondary  the  postulate  originates  either  pathways,  the  consistent  formed  there  (or  product  substituents the  18  that  successful  starting  final  during  biradical  on  the  is  the  reasonable  regioselectivity  reaction  Figure  Provided  BR-1  seems  properties  the  effect.  Effect?  depend  3  the  electronic  it  factors  influencing  w i l l 1  the  solution  These  in  proceed  formation  is  the  regiochemistry  continuation no  material  significant once  the  BR-2  i f  in  stereospecific  a  can of  a  1,2-aryl  therefore the  of  the  f i r s t  cyclopropyl shift  8  1 3  from  to  the  dicarbinyl  occurs^ ),  manner.  final  reaction  reversibility  originate  alternative  the  of  ^  it  The  must steric  differences  cyclopropyl  in  dicarbinyl  intermediates. possibility  conditions investigated pure  work  indicated  species  The  present  was  step. ^° ' ' excited  of  in  of  or  nature  the  found  effect,  Primary  the  used  inhibition  attached  Regioselectivity.  similar  trend  steric  steric  Solution  which and  the  having  could ruled  photoproduct  procedures,  of  facilitate  out. 63A,  starting  the  After under  material  photoproducts thermodynamic  long  photolysis  typical was  laser  recovered  being  formed  under  equilibration  was  periods and  lamp  unreacted.  of  samples  of  irradiation  -143-  Figure ents  in  A the  57.  primary  steric  regioselectivity  steric  the  the  give  by  of  effect  has  observed  9-position  of  stabilizing  of  the  Bridgehead  the the  favour  a  put  compounds  substituents  r e s u l t s .  been  1  in  of 2  4  this  electronic  It  has  mechanism  4  substituents  shown  case,  been in  involved ** • ( F i g u r e  benzylic  forward  (R)  Substitu-  previously  di-7r-methane rearrangement  participation  B R - 2 may b e  effect  S t a b i l i z a t i o n by  dibenzobarrelene  effects  obscured from  Center  BR-2  substituted  at  Radical  would  radical  in  that  postulated  which  a  57).  In  offer  center  were  the in  this  found  can  be  2  4  to  -p  n e  be  substituents  an  advantage  BR-2  1  discerned  1,2-aryl case  9-alkyl  5 8 .  that  direct  explain  the  Figure  however,  effects  of  to  without  shift  to  inductive of  further  having  to  -144-  disturb  the  vinyl-benzo radical  aromaticity  of  bridging  therefore  stabilizing  isotope  effect,  (Figure  58).  disfavor  the  even BR-2.  it  cannot certain groups Such  is  regular  state  nature be  so  the  brings the  the  an about  steric  the  same  determines  the  steric  increase a  modest  in  the  mixed  increase  in  the  size  in  an  even  the  when  a  such  a  to  the  in  B R - 1 . The  side  of  manifested  other the  hand size  of  species  the as  an  analog^  0  3  should of  this  the steric  "BR-l-like",  intermediate"^  m e c h a n i s m w o u l d make  BR-1  0 3  the  regioselectivity.  of  the  ester  substituents,  results  size  difference  in  diesters  in  be  "true  Our  one  the  importance  cyclopropyl  state  the  The  case  9-deuterated  intermediate  increase  increase  at  the  of  the  of  of  the  on  effect  in  can  bulky.  identified.  is  occur  effect  transition  case  results  case  circumstance  which  of  the  as  to  which  involvement  this  readily  point  tert-butyl 60:40.  from  under  in  ring,  favored  sufficiently  represents  transition  found  primary  becomes  Even  The  was  The  arises  i f  as  benzene  substituent,  formation of  substituent effect  is  the  of  the  the  alkyl  A:B  to  that  between  reaction  Me/Et-28 the  reveal  up  the  to  two  a  alkyl  regioselectivity.  Me/tBu-32,  groups  product  however,  in  from  ratio  from  which  ethyl 52:48  a to to  -145-  R P-Proximal  Bonding  R.~Remote B o n d i n g  Bonding Substituent  Proximal  Remote  53  47  29  71  23  77  D CH  3  (CH ) CH 3  2  ;  LCH3I3C 48  References  58.  Figure  Regioselectivity  Q  Involvement of  100  124.  and  The  Regioselectivity  the  of  a  Primary  Di-w-Methane  Steric  Effect  Rearrangement  of  on  the  9- Substituted  Dibenzobarrelenes.  Whether but  above  measurable  normal the to  the  procedure  photoproduct search  only  apply  reaction case.  for  *  a  in  center  change  in  primary  steric  would  to  ratio  linear cases  be in  effect  analyze  terms  of  correlation.  where  and not  product  the  the  ratio is  1  3  1  substituents  separated  by  a  Eg  These  C0  2  be  d i f f i c u l t  effect  Taft's  can  of  taken to  the  steric  directly  spacer  as  a  small  determine.  The  substituents  on  parameters  parameters, are  as  in  however, attached in  the  order would to  the  present  -146-  It  is  interesting  indicate  that  demanding  position  possibility the  the  look  to  like  and  the  character  the  among  state.  most  the  the  in  This  state  separate  lengthens  by  be  a  less  interaction  (which the away  would  reasonable  interactions  supporting  substituent  effect sterically  steric  These  transition  a  may  demanding  carbon  bond  steric  rests  themselves.  in  attached double  primary  substituent  that  after  vinyl  a  transition  extent  the  that  may  will  acquiring  be  probably  bulkier from  for  group  each  other,  single  bond  ( F i g u r e 59).  Figure  Possible  59. at  Besides indicate  the  arises  B R - l ) ^ b  short  Formation  at  some  rehybridizes,  note  bulkier  considering  substituents  relieved  to  the  Carbon  the  low  a  primary  that  remote  location  of  the  product  to  Me/iPr-30  of  and  from  Attached  of to  the  the  steric  effect  substituent.  to  further  1 2  Steric  Bulkier  regioselectivity,  the  ratio  Relief  8  These  branching of  Me/sBu-31 to  observations largely  include the  Me/tBu-32),  by  Bond  seem  to  Substituent.  other  w o u l d be  Interactions  diminished by the  insensitivity  substituents and  to  the  the  (Me/nPr-29 surprising  -147-  lack  of  an  effect  Me/iPen-34. menthyl  and  of  the  compounds  are  possible may  vity  observed  A  be  Secondary  An  between  the  indicated  Steric  be  a  the  =  as  of a  out  mean  to  that  is  this  relatively  large  and  observed  the  between  The  context  and  in  the  with  Me/Phe  the  and  neo-pentyl  consistent  regioisomers. within  Me/nPen-33  as  ethyl, the  poor  diester  37  a  of  result  phenyl  substituent.  reversed  regioselecti-  30:70)  the  groups of  1 8 0 ° and  the  may  system of  drive  a  cos 0 2  0 ° C and  has  and, a  as  the  depend  two  one  of  to  the  respect  that  resonance on  double  been  the  represented 9 0 ° .  to in  in  interactions the'  adjacent  v i n y l i c  double  stabilization  torsion  b o n d s . ^  proposed  minimum a t  observed  repulsive  keep  with  should  energy  the  and  suggest  the  regioselectivity  that  conjugation  planes  of  for  possibility  resonance  function  maximum a t  groups  from  explanation  alkyl  the  bulky  difference  arising  T h e o r e t i c a l models  the  dependence terms  by  size  analyze  effects  a./3-unsaturated by  to  and  equivalent  ester  two  compounds  Effect?  on  group  bond.129,132  defined  the  (70A:70B  two  small  sec-butyl  of  branched  effect  the  d i f f i c u l t  rests  carbonyl  an  39  alternative  solution  of  38  electronic  This  an  series.  and  substituents  highly  butyl  between  more  the  exert  or  discrimination results  larger  Furthermore,  isopropyl  the  the  derivatives  compounds In  of  angle,  8,  The  angular  in  relative  vary Figure  60,  w i l l  -148-  Figure as  a  Function  The in  60. of  Resonance the  Torsion  consequences  principle  reactivity  affect  levels.  dibenzobarrelene 1,2-triplet conjugated  of  the  diester  carbonyl  Angle  having  a  carbonyl  f i r s t that  (Figure  (carbon  1)  of  61).  Two  group the  concerns  can be  is  of  Conjugated  n-Systems  (6).  outcome  The  biradical  Energy  The  out  reaction the  radical to  conjugation from  excited  r e g a r d e d as  expected  of  a  a  different  state  resonance  center have  two  next larger  to  can  of  the  stabilized the  odd  least  electron  -149-  density ring the ment  which  attack.  of  conceivably  This  di-7T-methane  point  of  61.  The  1  Triplet  make  view  reactivity  dibenzobarrelenes  Figure a  can  is  with 3  3  it  more  consistent  the  well  (figure  Excited  reactive with  known  a  free  towards model  aromatic  that  radical  compares  rearrange-  62).  State  of  Dibenzobarrelene  Diesters  as  1,2-Biradical.  At  the  carbon  (carbon  stable,  reaction  the is  reaction  expected  seems  is  known  conjugation and  therefore between the can  ethyl  intermediates,  to  occur  delocalized,  regioselectivity  determine  methyl  1)  factor  conjugation may  of  resonance  s t a b i l i t y  It  level  the  observed be  of  to  two  play  a  decisive  substituted  possible  carbonyl  results.  regarded  it  1,4-biradical.  vinyl  quite  since  attack  Having  one  as  approaching  dibenzobarrelene  monoesters  generate  The  relative in  5  different the  the  •  1  3  found  the  0  vinyl  group  by  most  radical  degrees  situation  studied  •  central  carbonyl the  same  determining  compounds . ^  and  the  would  role  that  groups  by  of bond  out  of  in  the  Ciganek  and  -150-  C r i s t o l ° cases product  5  • ( f i g u r e  was  found  that  63).  to  proceeds  be  The  stereochemistry  completely  through  the  of  determined  more  stable  by  the the  product  formation  intermediate.  H  Cl3CBr  CC13  Figure  62.  Free  Radical  Rearrangement  of  Dibenzobarrelenes.  COOR  COOR  COOR  R  Figure  63.  Regioselectivity  in  -  Me,  Et  Dibenzobarrelene  in  Monoesters.  these of  the  -151-  Spectroscopic the  two  carbonyl  infrared takes  advantage band  difference's  6  2  ,  8  7  the  can  (see  between  s-cis  that  and  /  I  be  c r i t e r i a  page  lower  the  of  for  It  conjugation  obtained  has  at  conformers  can  bond  >  5.2;  I  between  solution  from  conjugation  which  been  carbonyl-double  double  in  assigning  frequency  87).  s-trans  include  s-trans  degrees  sometimes  normally  occurs  (I  a  different  Empirical  of  measurements  r a t i o  for  groups  measurements.  carbonyl  from  evidence  a  conjugated  postulated also  bond  s-cis  be  that  identified  intensity  /  I-double  (I)  bond  =  0.6-3.5).  The here  ene-dioate  is  between and  p a r t i a l l y 1750-1600  p a r t i a l l y  discerned with  at  difference  in  In  and  1705  the  the  an  substituent  frequency a  methyl  of  the  substituent.  the  inductive  late  group.  series the  of  alkyl  assignment  entire  mixed  Such  of  effect  diester  the  is ester  group  substituent  can  of be  in  bands  much is  as  illustrated  was  64  found  20  cm"  form  in  to  The  cannot  be  1  known  The  carry  that  stretching 1  relative  attributed of  be  located  the  operation  below.  can  cm" .  the  normally  resonance  Figure  be  is  range intense  1630  It  decreasing  as  two  unfortunately  effect  polar  nicely  shown  carbonyl series.  the  of  the  solvent)  at  conjugation.  studied  in  can  carbonyls  in  by  CHCI3  fragment  frequency  capable  system  Me/iPr-30, (in  vinylic  differences  benzoates the  diester bands  of  band  compounds  i n f r a r e d band  of  The  1  stabilization  This  case  cm" .  to  carbonyl  an  carbonyl  carbonyl  assigned  dibenzobarrelene  by  intensity  unambiguously isopropyl  the  the  overlapping  half  of  characterized cm-1.  1720  about  structure  to  carboxyin  uncertainty over  to  to  the in the  -152-  Figure Carbonyl  64.  Inductive  Frequency of  Alternatively, not  only  also  to  to  NMR  1  3  6  determine  r i g i d  claimed  ries  estimated analysis  spectrum Two  of  distinct  tively.  to  use  of  whether  been  provide  from of  the  diester  a  is  carbonyl  Substituents  on  the  C  3  also  conjugated  t o r s i o n NMR  in  the  compare  1 3 5  1  3  5  ,  1  3  6  and more  case  well  been  of  with  the  proposed  or  not,  but  angles recently latter,  gas  phase  in  the  of 1  7  0 it  geomet-  methods.  carbonyl was  actually  1  and,  that  f i e l d  group  bond  Both  applied  Me/iPr-30  were  Alkyl  has  values  force  the  NMR s p e c t r o s c o p y  carbonyl-double  have  bands  of  Benzoates.  compounds.  techniques  was  An  the  determine  relatively  Alkyl  Effect  carbon  resonances  carried  out  found  at  165.9  for and  exploratory 164.6  ppm  1  3  C  NMR  purposes. respec-  -153-  In carbon  the is  of  normally  relative tion  case  C NMR s p e c t r o s c o p y  expected  shielding  c o n t r i b u t e d by  to  resonate  originates the  with  resonance  -C=C-O0  at  the  the  higher  >  order  between  the  differences diesters  a  two in  The  carbonyl  and  spectra  carbonyl  -C -C-C-0 +  C  carbonyl  carbons  ppm)  found  2 v  of  to  observed  in  indicates  that  the  in  30  resonances  the  substituents. NMR  experiment,  The  gas  obtained the  global  were  resonance in  diester  spectrum  due  1  3  -  ^  3  e  d e r e a l i z a -  _  also  each  the  the  two  obtained  carbonyl  of  due  the the  found  spectra  to  same to  solvent  contain  of  and  iPr/iPr-23:  the  two  chemical  chemical  shifts effect  within in  30  of  the  the 164.7 shifts  result  clearly  of  the  carbonyl  the  two  different  time  have  a  indicated  shift  This  such  symmetric  that  chemical  Me/iPr-30.  groups  was  shift  165.8  of  that,  chemical  in  were  The  inductive  conclude  spectra  overall  case.  in  Me/iPr-30  diesters  compound in  to  also  (Me/Me-18:  with  difference  the  and had  each  unsymmetric  is  of  symmetric  correlate  the  scale  of  the  indistinguishable  geometry.  phase  from  the  each  electronic  difference  d e r e a l i z a t i o n ,  symmetry  We c a n  d e r e a l i z a t i o n  of  the  carbons  iPr/iPr-23  carbon  time-averaged  was  whether  electronic  strength.  I I  determine  Me/Me-18  (CDCI3). single  to  carbonyl  II:  I  In  conjugated  f i e l d  expected  structure  <  more  molecular  molecular  energy  minimum  conformation  mechanics as  a  of  several  (program M M P 2 ) .  function  of  the  diesters 1 3  ^  In  carbonyl  order system  was to  also obtain  conforma-  -154-  tion,  the  variation -  •a  energy  of  of  two  the  a  large  49  different  the  dihedral  dihedral rotated every  angle 360°  step.  resolution, in  Figure  It 30",  an  24  =  was  in  factors already alkyl An  cannot  determining  the  contained  to  place  in  the (e.g.,  order  the  to  by  the  1  01)  the  same  carbonyl  Et/Et-21 may  of  not  the  groups  carboxylate  ester  7  use  of One  0  (82)  was  with  at  this shown  conformation  (01  iPr/iPr-23). a  very  This  important  system.  planarity  groups  =  significantly  ene-dioate of  81  conformation  play  out  65,  rotamer  covered  with  and  3  other  different  diesters  group  carbonyl  a  carbonyl  that  conjugation  two  p r o g r a m .  while  by  structure  computer  Me/Me-18.  alkyl  The  by  compound  the  (Figure  obtained  conformations  (Me/Me-18,  the  angles  was  obtain  minimum i n  the  calculated  regardless  The  may  be  of  the  substituent. interesting  system be  observation  where  both  are  involved  drawn  deconjugating  one  energy,  may n o t  ing  two  the  as  substituents that  structures, dioate  the  reached  rotamers)  possible  interesting  tend  of  minimum d e f i n e d for  dihedral  was  0(4)-C(15)-C(12)-C(ll).  in  the  suggested  that  bond  constant  a l l  found  alkyl  =  conformations  (carbonyl  increments  energy  very  observation role  30°  2 1 0 ° ) was  different  82  f a c i l i t y  kept  Within  was  82  driver  was  in  and  conformers  angle  of  carbonyl-double  0(2)-C(13)-C(ll)-C(12)  of  number  be  at of so  carbonyl  carbonyl in  the the  comes  high  at  with  time.  carbonyl  given  systems  groups  resonance  same  two  from  the the  It  the of  the  the is  possibility time.  that  resonance  cross-conjugated central  possible  groups,  same  fact  in of  double  that  terms  the  enebond,  cost  of  of  resonance  p a r t i a l l y  delocaliz-  -155-  The  suggestion  may  exist  NMR  data  methyl  independently obtained.  and  carbonyl  the  required  isopropyl  order  conjugation  as  ment  be  must  shorter whose  then  diesters excited  ester  f u l f i l l e d :  are  present  may  not of  work.  Stern-Volmer  it  the  30  in  excited  the  M benzene  From  a  kqr  =4.86  lifetime  of  x  9  sec  was  the  triplet  From  the  standpoint  secondary  steric  conformer  lifetime  C=C-C=0  10"  single  of  effect  range.  biradical  intermediates so  far  This  are  be  lifetime  known  in to  using 1  the  of  3  two  Any  such  the  time  carbonyl  1  kq 3  of  the  triplet  course was  5 X  of to  di-jr-methane short  10  order  indicated  also  the  of  the  measured as  M "  9  by  1  the  sec" , 1  a  9  in  rates  of  dibenzobarrelene  the  =  be  intermediates  lifetimes  the  30*  should  1,3-cyclohexadiene  and  one  extremely  the  require-  conformer  lifetime  state,  may  the  another  reaction  during  required  range  the be  case  triplet  the the  or  the  M "  than  factor, diester  o b t a i n e d .  as by  would  nanosecond  observed  such  (determined  bonds)  the  measured  of  adopting  the  both  differential  Although  available,  quencher. 1.0  a  8  explain  minimum.  of  state 3  in  triplet  ca.  1  minimum  experiment.  controlling of  may  shorter  possibility  was  0.1  turns  energy  NMR  i n f l u e n c i n g .  lifetime  kinetics  the  group  e q u i l i b r i u m where  lifetime  intermediates  diester  the  lifetime  presently  The  take  the  the of  be  groups  a  conformational  alkyl  rapid  in  stereochemical  the  a  have  the  lifetime  of  define  detection  diradical  state  that  eliminate  behavior  di-7r-methane  nature  to  the  non-conjugated  requires  should  discrete  same  the  This  however,  for  the  of  conformations  conformer,  In  that  to  in  Figure  rotation be apply  longer to  In  61,  a the  around  the  than  the  the  rearrangement lived.  observe  triplet  since  the  in  those  case  of  -156-  th e 162),  naphthobarrelene a  lifetime  experiments-  1 0  Without determine  effect.  rates  the can  of  X  10"^  of  sec  rotation  lifetime  However,  probably  20  by  Shaffner  was  et  measured  a l . by  (Figure flash  67,  page  photolytic  •  the  conclusion  of  studied  73  the  of  the  be  drawn  the  extremely  triplet  about  around  the  ene-dioate the  short  biradicals,  C-C-C-0  conformers,  involvement  lifetime seem  to  single  of  of  the  a  bonds, no  which certain  secondary  triplet  make  this  a  the  Ene-Dioate  steric  state,  viable  and  hypothe-  sis.  Figure  65.  Gas  Dibenzobarrelene  Phase  Diesters  Conformation as  Obtained  of  from Molecular Mechanics  System (MMP2).  in  -157-  The  Regioselectivity  The  Materials.  It  is  factors to  for  our  of  Attempts elucidation several  the  mentioned  before,  to  trying  to and  extremely  thin  Me/iPen-34  was  procedures  molten  Compound  Me/neoPen-35,  presented  properties  Me/Et-28  and Me/nPr-29  as  required  for  Finally,  softening  a  a  that  of  have  ambient  different In  order  reactivity  we  crystal  and  molecular  suitable  for  structure  of  turned  in  instead were  structural  also  found  devoid  agreement of  a  sharp  analyzed  and  to of  (both  which with  to  analysis.  a  found  not  to  A sample not  needle  be  like  in  the  exist  as  diester  material.  transparency, structure  point.  Some  X-rays  Et/iPr-38  fully  with  crystals  diffract of  as  diesters  The  similar  glassy  melting  Me/sBu-31,  storing  crystalline  could a  on  of  materials  and  out  give  with  determination.  structure  crystals  diffraction  use  Me/Menthyl-36,  solidified  Et/sBu-39  the  promising  and  months.  for  involved  Me/iPr-30,  20  12  and  and  and  that  temperatures,  spontaneously  material were  disordered  suitable  at  unsuitable  long  to  Me/Pen-33  periods  a  found  Compounds  Me/tBu-32 plates  state  I n i t i a l l y  Me/nPr-29,  liquids  over  materials.  Me/Et-28,  Me/neoPen-35  the  X-ray  crystallization  recrystallized  range  the  solid  materials  of  that  56  regioselectivity.  controlling  obtain  Figure  crystalline  were  diesters  state  in  employed.  compounds  solvent  solid  to  Et/iPr-38.  and  of  The  factors  us  and  absence  possible  obtain  Me/Ph-37  summarized  and  to  for  State.  results  substrates  solvents  Me/iPen-34  the  Solid  the  led  obtained  the  solution  efforts  structures  were  from  determine  look  turned  clear  in  was  resolved.  morphology)  were  -158-  found  for  compounds  structures these  were  two  line  the  In  analogy  (dimorphs the  I  diesters  different  now  be  solid  Factors  the  for  state  analyzed  information  the  9  ,  1  4  carbonyl crystal If  in  which  f u l l  photochemical  detail  obtained  to  into  see the  crystal  results  for  i f  can  we  other  crystal-  the  the  the  vinyl  (dimorphs are  with  the  I  the  double  angle  II),  two  central  groups  bonds,  and  the  solid  dihedral  Me/Me-18, the  characterized  determined  carbonyl  in  compound  "freezes"  regioselectivity  by  of  Me/Ph-37  that  verification  and  between can  the  seems  be  structures  possessing  carbonyl  double  by  state.  by  Et/Et-21  groups  bond.  The  relative  to  be extent  the  mean  estimated  radical-  of  to  conjuga-  planes from  at idea  amenable  The  a  of  the  the  X-ray  structures.  factor  would  least  a  v i n y l  proceed  stable,  attack carbon  carbonyl  secondary  in  conjugated  guarantee  reactive  and  of  State.  structure  conjugation  conjugation,  reaction  would  of  Solid  iPr/iPr-23  Me/iPr-30  defined  0  determining  the  and  abilities  experimental 7  the  II)  extents  having  t i o n ,  with  in  conformation  delocalizing  more  The  structural  and  disymmetric  of  w i l l  Me/Ph-37,  compounds.  Stereoelectronic  of  and  determined.  compounds  extrapolate  Me/iPr-30  the by  solid  bond  carbonyl to  the  center  steric state,  formation group  (see  aromatic (Figure  delocalized,  effect,  61)  at  one the  would vinyl  above). ring as  were  by  well  1,4-biradical.  as  the  predict  carbon  product that  attached  This  reaction  the  expectedly  the  The  the  pathway  formation  predicted  to  more of  the  reaction  -159-  pathway  and  experimental 66.  Three  borrowed  observations more  from  Figure (66).  photoproduct on  examples,  other  sections  of  diesters  the  rearrangement  23  (dimorph  of  the  thesis  30  I), are  and are  37  along  presented  (R,S)-42 included  and in  with in  the  Figure  (S)-(+)-42, the  same  -160-  Compound Rl  62  61  R2  iPr  Me  cos t?l  cos 02  2  2  predicted  observed  315.5  143  4  0.51  0.64  A  B  Me  Phe  225.1  214  7  0.50  0.68  A  A  iPr  iPr*  164.3  63  7  0.92  0.20  A  B  iPr  (S)-sBu  166.2  68  4  0.94  0.14  A  B  iPr  ( R . S ) - s B u 167.4  70  1  0.95  0.12  A  B  * II)  Pathway  Regioselectivity  and  by  Figure Predicted  analogy  66. and  with  obtained  from  isomorphic  Stereoelectronic  absolute  crystals  Effects  Observed Regioselectivities  Dibenzobarrelene  Diesters.  of  of from  configuration iPr/sBu-42  the the  Carbonyl  studies  (see  Part  Groups  Di-rr-Methane of  on  (Part IV).  the Some  -161-  The  angles  dihedral  or  of  each  double  bond.  function  of  atoms  in  lie  8  The  the  (Me/Ph-37)  with  A very that  the  have  our  4  and  the  the  of  the  those  from  the  groups  of  Me/iPr-30) only  as  the  p-orbital the  with  maximum v a l u e  60). A l t h o u g h  (i.e.  defined  central  the  when  cos^  a l l  the  difference  in  the  compounds  to  large  agrees  in  one  in  (i.e. case  expectations.  observation  from  the  two  contributions  than  the  value  carbonyl  a  are  varies  regioselectivity  mechanistic  of  before,  delocalization  of  system  carbonyl  small  66  planes  and  reaches  (Figure  0  very  mentioned  one  1  of  Figure  mean  groups  adjacent  iPr/sBu-42),  more  partial  having  two  energy  given  in  the  carbonyl  p l a n e  from  sum o f  As  (1.0).  same  interesting  slightly  between  two  angles  the  and  tabulated  resonance  ranges  66  82  angles the  the  iPr/iPr-23  is  of  between  Figure  and  "twist"  lobes  cos  81  one  the  at  the  perfectly  the  cos 0  adds fully  up  to  a  in  value  conjugated  ene-dioate two  values  2  system  carbonyl  conjugated  and  Figure of  carbonyl  clearly  groups the  1.1,  is  which group  prefers  rather  other  66  to  than  perfectly  orthogonal. It  is  interesting  stabilization as The  to  has  determine  the  photochemistry  Shaffner  et  a l  1  8  was  been  to  notice  proposed  presence of  the  or  to  that be  precisely  sometimes  absence  unsaturated studied  the  of  this  of  sufficiently  di-jr-methane  carbonyl in  lack  compound  context  73,  resonance important reactivity. studied  (Figure 67).  by  Figure  Differential  67.  Non-Conjugated  The matrix  infrared at  stretching the  two  which of  Rotamers  77K  was  bands  carbonyl  the  changes  former was  of  Photochemistry  Benzoyl  spectrum found at  to  1633  conformers was  found  observed  in  of  and  two 1644  73-conj to  be  the  the  Naphthobarrelene  compound  show  from  the  73  in  a  distinctively cm"-'-.  These  well  bands  73-unconj  most  abundant when  the  and  73.  methyl  and  spectrum  Conjugated  tetrahydrofuran  defined were  carbonyl  attributed  respectively, component.  matrix  was  7 1  A  to  from series  photolyzed  -163-  at  low  temperature  and  then  important  aspect  of  discussion  is  only  band  affected  was  This of  result the  even  that  was  starting  material  Although  to  is  not  not  reaction  Clearly, in  case 63.  the  of A  et  having solid  having  inductive  only  hydrogen  on  of  substituent  the  two  does one  not  arise  the  unconjugated  in  the  observed  that  naphthobarrelene  the  recovery  bands  to  in  case  Figure  the 66.  degree  of  the  radical  arise or  78,  contrast  should  be  (intramolecular)  stabilization  may  of  conjugation  It  internal  differ-  In  of  reactivity.  from in  the as  perfectly  in  the  factors.  differences the  quantum  of  conjuga-  carbonyl  the  can g r o u p  Figure  63.  shown  monoesters  from  stabilization  of  out  reactivity  primarily  monoesters  reactivity  authors  the  almost  group  radical  exclusive  conformers.  parallel  of  processes.  coefficients)  group  arises  present  subsequent  for  in  hand,  the  frequency  speculative  from of  other  carbonyl  with  most  7 1  compounds  carbonyl  carbonyl  The  The  lower  carbonyl  included  (extinction  difference  degree  effects  the one  the  remain  involvement  light  state  fundamental  substantial  results  a l . ,  of  of  diester  the  the  accounted  dibenzobarrelene  the  of  experiments.  diesters  dark.  non-conjugated  clearly  to  for and  78-Conj.  the  the  connection  indication  assignment  the  of  an  has  in  photochemical  the  the  our  Schaffner  or  of  in  responsible  conformer  the  of  require  absorption  yields  tion  case  that  and  end  in  affect  out  of  the  as  species  case  the  to  comparison Those  the  and  definitive  the  in  78,  pointed  in  a  the  conjugated  seems  species  photolysis  inert  warmed  observations  during  exhaustive  remained  this  the  interpreted  species  ently  those  carbonyl-conjugated  after  slowly  be 1  4  1  in of  Figure  fact  that  expected  by  relative  the  to  a the the  -164-  Solid  State  Most  Primary  solution  related  to  such can  two  approach either  it  solution  larger  non-bonded and as  are  than  the  the  operating solid  and  mechanism  and  Analysis models  bonding From  occur of  the  step, an  we  fixed  crystal  during  most  the  two  decided  original  to  arise  in  between  anisotropic  the  organization  of  effects  are  essentially  Scheffer be  et  are  al  have  cyclopropyl  on  process  2.43  A ,  1  the  the  in ^  3  the  latter,  the  reacting  the  1  1  In  solvent in  a l l  determined  by  r e q u i r e d by  the  how the  specific reaction  determined. " 3  based  ring-forming  primarily this  in  difference  the  both  well  mechanism changes  di-fr-methane  intermediates  shown  when  reasonably  dramatic  about  motions  identified  reaction  analyze  the  that  approach  identical  specifically  and by  forces  surroundings.  for  be  of  that  the  depends  distance  the  of  can  the  of  This  fundamental  is  were  closely  energy".  most  may  so  lifetimes  structure  reaction  The  w i l l  di-w-methane  other  case  factors  repulsive  the  structures  effects  the  by  solution  3  3  steric  each  effects  and  Lazar, -  mechanism(s).  that  in  in  intense  compression  steric  environment  the  indicates  structure success  of  "the  as  defined  effects  approach  or,  required  molecular  the  as  2  interactions  by  time  steric  Steric  atoms  state  Compression.  necessarily  intramolecular.  solid  state  reaction  state  be  suggested the  are  non-bonded  relatively  Solid  crystal  1  repulsive  molecular  directions.  Shorter ^  non-bonded  and  its  solution, longer  by  can  Steric  structure.  intermolecularly  between  and  effects  originates  rearrangement,  molecule  steric  defined when  occur  Effects.  molecular  adequately operating  Steric  on  molecular  dibenzobarrelene steps. f i r s t  Since  the  aryl-vinyl  detail. reacting  vinyl  and  -165-  aromatic  carbons  approximately substituent  1.54  attached  displacement cause  the  must  in  the  direction  of  molecules  in  the  amount  of  be  surrounded  non-bonded  have  different  when  one  more  than  magnitudes.  reaction an  mechanism  alternative  68.  The  Step  this  bonding  (Figure  different  fixed  the  lattice  energy  This  of  place a  the large  motion  atoms  of  the  process may  may the  ester  environments,  each  of  takes  non-equivalent  regioselectivity  the  distance  undergoes 68).  accompanying  reaction  increases  carbon  Since  bond  process  relatively  crystal.  energy  single  the  may  also  originate  transition  state  one.  Displacement  Bridging  C-C  vinyl  the  by  repulsive  a  when  moving  push  should  Benzo-Vinyl  to  to  groups  to  Notably,  A.  the  together  substituent  neighboring  Figure  come  of  the  on V i n y l  Vinyl-Attached Disubstituted  Substituent  During  Dibenzobarrelenes.  the  -166-  The  packing  differences  around  each  of  t h e e s t e r groups o f t h e  d i e s t e r s M e / i P r - 3 0 a n d Me/Ph-37 c a n b e  visualized  i n Figure  large  neighboring  molecules a t contact  spheres  distances  represent  o f l e s s t h a n 3.0  Qualitatively, surrounded  the methyl  than  respectively.  the  The  atoms A  from  ( t h e hydrogen and  isopropyl  phenyl and  regioselectivity  atoms  ester  methyl observed  l a r g e r motions from p a r t o f the l e s s t i g h t l y  are  not  g r o u p s a r e more groups  i n 30  69.  The  shaded). tightly and  37  i s i n agreement w i t h t h e surrounded  isopropyl  and  m e t h y l g r o u p s o f 30 a n d 37 r e s p e c t i v e l y ( F i g u r e 6 3 ) .  Me/iPr  Me/Ph Figure  69.  L a t t i c e Environment Around t h e V i n y l  d i e s t e r s M e / i P r - 3 0 a n d Me/Ph-37.  Substituents o f the  -167-  A l t h o u g h the qualitative  free  lattice  approximation,  space concept can a  1 4 4  more  mechanistic problems of s o l i d  state  Quantitative  pointed  conveniently  approaches, b a s e d on  intermolecular me t h o d s .  3 0  -  1 4 4  as  The  instead  energy  potential  e n e r g y b e t w e e n an  (PPE,  same m o l e c u l e i n t h e  6,12  Eq  14))  that  1 2  of  the  comes f r o m t h e  phenomena  that  as  gas  packing  difference  phase 3  and  in the  4 4 d  14.  i t results effects  also  the  from  in  size:  that  the  state  the  same  exactly  chemically  same  solid  reacting  give  Van  der  meaning  Waals  systo  interac-  1 4 5  meaningful  to  consider  s u r r o u n d i n g s o f the  energy  the  parameter to a n a l y z e the  m o l e c u l a r s h a p e and  When i t i s e x t r a p o l a t e d  the  the  steric  3  tions.  non-bonded  (Kcal/mol).  as  t e m s . 0 , 1 4 5 T h e s e phenomena a r e such  be  in A  fact that  controls  the  can  1 4 4  lattice. ^>1  Eq  6  PPE  reactivity  its crystal  2(r*/r) ].  « - depth of p o t e n t i a l w e l l  concepts  to  quantum m e c h a n i c a l  describes i n the  first  desirable.  Gavezzotti,  rigorous  i s o l a t e d molecule  r* = equilibrium distance  choice  highly  semi-empirical  on  a  approach  is  by  formally  environment of  -. . e [ < r * / r ) . . -  The  out  as  most u s e f u l p a r a m e t e r i n t h i s c o n t e x t i s t h e  potential  v  reactivity  of  useful  quantitative  calculations involving  potentials  be  is  calculated  molecules with  respect  to problems of chemical  the  PPE  as  a p o t e n t i a l energy f i e l d  reacting molecule. between to  their  reactivity,  every  I n e q u a t i o n 14  atomic  relative  pair  positional  of  the two  i t  is  defined  by  potential interacting  parameters,  the  -168-  interatomic distances ( r ) . type the  [given  by  1  4  the term:  The  6  dispersion attractions  2(r*/r) ]  and  6  the f i e l d  in  the c r y s t a l ,  whole.  3 0  -  positions  a  (r*/ )^] r  d e f i n e the  magnitude  and  after  complete  the  molecules  summation,  for  are  at  the  crystal  as  reaction,  i n the parent c r y s t a l  perfectly  balances  more  stable  and  the  found magnitude  the magnitude  their  equilibrium  the  attractive  of  o f the r e p u l s i v e ones.  When a  i t can undergo atomic d i s p l a c e m e n t s i n  search  excited  state  geometry.  While the  electronically  e x c i t e d compound r e a c h e s t h e t r a n s i t i o n s t a t e o f a c h e m i c a l r e a c t i o n will  undergo atomic d i s p l a c e m e n t s w i t h even  i n which  l a r g e r a m p l i t u d e s . The  a n e x c i t e d compound r e a c h e s t h e p o t e n t i a l  reaction  while  structural  in  geometry  A l t h o u g h any  the  solid  state  energy  surface  and by c h a n g i n g i n t o a  has been c a l l e d dynamic p r e f o r m a t i o n .  s u c h d i s p l a c e m e n t w i l l be  energetically  comparatively forbidden. This results  repulsive function  energy  Several  of  potential of  in  Jones p o t e n t i a l  the  the  r  1  2  1 4 7  motions  reactivity.  energy  often  in  energy invoked  1 4 4  f u n c t i o n s have been used t o d e s c r i b e the  positional  atomic  parameters.  1 4 6  The  e q u a t i o n 14 i s commonly r e f e r r e d t o a s t h e " 6 - 1 2 " f u n c t i o n a n d was  will  increase  dependence o f the p o t e n t i a l the  a  favorable  costly,  sharper  the reason f o r the need o f  f o r chemical  i n terms  presented  to  and e x p l a i n s  1 4 6  "empty s p a c e "  PPE  due  from the  i t  event  t h a t s t e e r t h e atoms o f t h e r e a c t i n g m o l e c u l e a g a i n s t i t s n e i g h b o r s be  by  f o r e v e r y atom i n t h e r e a c t i n g m o l e c u l e , f o r e v e r y m o l e c u l e  molecule absorbs a photon of  London  1 4 6  Before  forces  the  the r e p u l s i o n f o r c e s caused  o v e r l a p o f e l e c t r o n c l o u d s [ g i v e n by:  of  of  t h e one  used i n  the  present  function Lennard work.  1 4 7  -169-  The  approach  used  in  t h i s work c o n s i s t e d i n c a l c u l a t i n g  f u n c t i o n o f the atomic displacements r e q u i r e d  i n following  o f t h e assumed di-jr-methane r e a r r a n g e m e n t m e c h a n i s m . t h e s e c a l c u l a t i o n s , p e r f o r m e d b y Mr. be  found e l s e w h e r e . The  plots  t h e PPE  Fred Wireko  The  4 6 , 4 7  of t h i s  the  motions  details  department,  i n F i g u r e 71 i n d i c a t e  that there  i s a rise  i n the  the  of these motions  vinyl  fragment  e n v i r o n m e n t . The of  an  moving  aromatic  c a r b o n s . The  mechanics  f o r computational purposes and  a  perfectly  rigid  motion o f each v i n y l  operational  vector  joining  by  Figure  70.  can  direction  considering  a r o m a t i c framework  c a r b o n was  simulated  a and by  of have  flexible lattice rotation  the b r i d g e h e a d carbon, n e x t t o the  fragment of the molecule, to the v i n y l  the double bond  of  i n the  p o t e n t i a l e n e r g y as e a c h v i n y l c a r b o n i s d i s p l a c e d  been s i m p l i f i e d  a  1 4 3  shown  neighboring  as  c a r b o n a t the o t h e r end  of  (Figure 70).  Simulation  Di-jr-Methane Rearrangement  of  the  Aryl-Vinyl  Bridging  of Dibenzobarrelene Diesters.  Step i n the  -170-  Displacements negative was  are  labelled  (counterclockwise)  calculated  at  2"  p a r a m e t e r s d e s c r i b e d by  Hagler,  that four d i s t i n c t  accounts  for a different  curve  represents  d e g r e e s as p o s i t i v e  according  intervals  noticed  each  in  to the sense o f r o t a t i o n .  with Huler  operations  solid  equation and  and  14  Lifson.  c a n be  1 4  made a n d  state reaction  the energy p r o f i l e  each e s t e r group. P o s i t i v e  (clockwise)  by ^  group.  however,  I n the  we  only  case have  of  'It  taking place at either v i n y l results  shown  in  Figure  results  and  respect  to the displacement  carbon, 71  are  i n d i c a t e t h a t the r i s e  g r o u p i n compound 30  and  diesters  experimental  should  t h a t each of  pathway.  In  on  the  Me/iPr-30  results  side of  and  in  agreement w i t h the packing  group i n  of  axis the  that account f o r motions  potential  37.  The  experimental energy  of the e s t e r groups i s l a r g e r f o r the  f o r the phenyl  71,  Me/Ph-37,  or r e a c t i o n r e g i o s e l e c t i v i t y . in  them  Figure  horizontal  r* be  a c c o m p a n y i n g t h e movement  negative values  the  PPE  u s i n g the  r e p r e s e n t s movement o f t h e e s t e r g r o u p i n q u e s t i o n t o e i t h e r vinyl  The  or  with methyl  -171-  Blown-up Profile of i P r 1 200i  300-1  -100-1 Angles  i n  Degrees  1  •  1 0  Angles  i n  Blown-up  g ^  ^ <J  2 HJ  5 0 0-  250n  400"  200-  300  150  200  100  100-  \  1/  H O CU  -100  -16  0  Angles  i n  Figure 71. P l o t s During  the  First  16  •  -16  Degrees  Profile  of Me  50-  -50  Degrees  o f Change i n P a c k i n g  -16 Angles  Potential  0  16  i n  Degrees  Energy  S t e p o f t h e Di-rr-Methane Rearrangement  r e l e n e s M e / i P r - 3 0 a n d Me/Ph-37.  • > 16  Resulting  o f Dibenzobar-  -172-  Regioselectivity  W i t h the iPr/iPr-23  Part  a i d of absolute and  pathways can II).  its  The  the  first  now  in  the  hypothesis The  iPr/iPr-23,  could not  a  our  a t t e m p t t o answer t h i s corresponding  included  in  substantially  to  Figure  steeper  attached  to  C(12),  result  supports  our  initial  having  a  agrees w i t h diester  is  conclusions  iPr/sBu-42  (see page  c o u l d be  chiral  119,  regarding  the  posed  dimorph  indicate  that  increase  in  in  the  during are  compression  which  based  involves  on  of  motions  compound at  configuration  energy.  the p r e f e r r e d s o l i d  These  IIP)  results of  the  s t a t e pathway.  This  the  motions  the  observation  of  i s o p r o p y l e s t e r group,  and  drawn f r o m s t u d i e s on 201).  (page  state steric  (absolute  suggestion,  two  question.  l a r g e r f r e e space around the C(12) the  results  C(ll)  s u g g e s t t h a t pathways 2 i n F i g u r e 49, ester  found that  o b s e r v e d p h o t o p r o d u c t ? We solid  the  72,  to  dimorph  i s o p r o p y l e s t e r g r o u p s moves  c o n d i t i o n to t e s t apply  plots  chiral  a n s w e r i n p a g e 119  r e a c t i o n to g i v e the  i s o p r o p y l e s t e r group a t t a c h e d cause  two  the  p h o t o p r o d u c t , we  state photochemical  which o f the  o f the  i n an  PPE  we  active  c o r r e l a t i o n shown i n F i g u r e 49  manner: step  solid  question  iPr/iPr-23.  c o n f i g u r a t i o n s t u d i e s on  optically  e x p l a i n the  reactant-product following  i n C h i r a l C r y s t a l s of Diester  isomorphic  crystals  of  -173-  Legend  1 2 0 0 -,  60-|  Potential  O C ( l l ) •  1000 -  for  C(12)  Energy  Reaction  P r o f i l e  at C(12)  40  800-  600-  20>-  W a:  400  UJ  2 u  f  200  H O  -200  •24-16-8 Angles  Figure  0 i n  8  16  16  i n  24  Degrees  Step o f the Di-7r-Methane  iPr/iPr-23.  State Results a t Large.  materials  state  results  studied,  group  are analyzed  i n  the  s e v e r a l g r o u p s o f compounds  according to the regioselectivity largest  - 8 .0  Angles  72. C h a n g e s i n PPE D u r i n g t h e F i r s t  When t h e s o l i d solid  •24-16  Degrees  Rearrangement o f D i e s t e r  The S o l i d  -20  24  observed.  The  most  context  o f the  c a n be r e c o g n i z e d interesting  and  i s made up o f t h e d i e s t e r s M e / n P r - 2 9 , M e / i P r - 3 0 , M e / s B u - 3 1  -174(racemic), crystals  Me/sBu-31  ( o p t i c a l l y pure),  o f these m a t e r i a l s  Me/iPen-34  the  similar size of their alkyl  substituents.  The compounds t h a t r e v e r s e the  solid  structural  state  features  can  derivative  18 s h o u l d  mentioned  before,  material. vity  exception  t h e s o l u t i o n s e l e c t i v i t y when  irradiated  classified shared.  c a n be i n c l u d e d  probably  34 ,  relatively  be  be  of  by  i n a second group where fewer The m i x e d  diesters  i n t h i s category.  classified  alone,  i t seems t o f o r m a g l a s s y r a t h e r  respect  Me/Et-28,  The  neo-pentyl  since  as  than a  crystalline  P h o t o l y s i s o f t h i s m a t e r i a l does n o t a f f e c t t h e  with  The  the  are probably  Me/tBu-32 a n d E t / i P r - 3 8  Et/sBu-39.  a r e c h a r a c t e r i z e d by enhancing the s o l u t i o n  r e g i o s e l e c t i v i t y and, w i t h  in  and  i t  was  regioselecti-  t o that observed i n the s o l u t i o n media.  Finally, i t  seems t h a t t h e s t r u c t u r e o f t h e p h e n y l s u b s t i t u t e d d e r i v a t i v e 20  should  share  should  very  little  a l s o be c o n s i d e r e d  i n common w i t h separately.  That t h i s c l a s s i f i c a t i o n appreciated  by  The s u b s t i t u e n t s n-propyl,  is  very  i n this  group  lar  forces  compounds s i z e and compounds,  not  vary  and s e c - b u t y l  be  totally  from  methyl  to isopentyl.  t h e s i z e (volume) o f the a l k y l  similar  1 4 4  .  artificial o f the f i r s t to  ethyl  groups  and  under  t h e s i z e and shape o f t h e  determine  the  crystallization  having  It  o f the  seems  therefore  possible  that  should  dibenzo-  intermolecuof  a r e determined by f a c t o r s r e l a t e d t o the molecular shape^O.  from  comparison  entire  behavior  be  group.  With exception  m o l e c u l e . F u r t h e r m o r e , i t i s known t h a t t h e weak that  can  I t c a n be e x p e c t e d t h a t t h e s e s u b s t i t u e n t s  a l t e r almost i n s i g n i f i c a n t l y barrelene  may  t a k i n g a c l o s e r l o o k a t t h e members  isopropyl  pentyl residue,  t h e r e s t o f t h e compounds a n d  the  organic  structure, mentioned  s o much s t r u c t u r a l r e s e m b l a n c e , may c r y s t a l l i z e  with  -175-  some common s t r u c t u r a l structure.  Some  support  found i n the very spectra  f e a t u r e s as v a r i a t i o n s  interesting  structure  of  observation that the s o l i d  The l a c k  compound  Me/iPr-30  group.  indication  The  The r e s u l t  operation) crystal  (for which a f u l l  relatively  1,2-methyl s h i f t may  not  structure.  high  crystal  the  large  f o r X-ray  i n  the  quality  crystals  o f 3 0 , may s t i l l  o f 2 9 . I t seems p o s s i b l e  that  given  p h i c e v e n i f somewhat d i s o r d e r e d . K i t a i g o r o d s k i solid  entire  state  from a d e l i c a t e  by  a  similar different  interactions,  the  and  i s an  t h a t o f 29 b y a  of a totally  will  o f the  crystalline  be e n e r g e t i c a l l y  t h e m o l e c u l a r c h a n g e t h e new s t r u c t u r e  some  was o b t a i n e d )  obtained  o f 30 i n t o  formation  crystals  compounds  Perhaps most o f t h e i n t e r m o l e c u l a r  to  of  model w i t h i n  ( o r o t h e r s i m i l a r compound  result  those present i n c r y s t a l s  result  suitable  X-ray structure  o f modifying the structure  as  that  infrared  crystallization.  o f s t r u c t u r a l homogeneity throughout the  hypothetical  size  state  t o continue speculating by supposing that  may r e p r e s e n t t h e i d e a l s t r u c t u r a l  phase.  o f more m a t e r i a l s  requirements f o ri d e a l  i s interesting  first  h y p o t h e s i s may b e  d e t e r m i n a t i o n i s perhaps n o t a m i s f o r t u n e b u t an i n d i c a t i o n o f  stringent It  speculative  crystal  o f t h e s e compounds ( e x c l u d i n g 34 a n d p r o b a b l y 3 9 ) s h a r e a  n u m b e r o f common f e a t u r e s .  the  f o rt h i s highly  a r o u n d an optimum  favorable  relatively  analyze  composed racemic  of  another  others  have  iPr/sBu-42.  shown  phenomena s u c h a s i s o m o r p h i s m a n d d i s o r d e r may  energetic  set of  compounds  small  t e n d t o be isomor-  compromise.  The s p e c u l a t i o n p r e s e n t e d h e r e may g a i n t h e r a n k o f h y p o t h e s i s we  such  closely  iPr/iPr-23,  related optically  and isomorphic active  when  structures  iPr/sBu-42  and  -176-  PART I V .  STUDIES ON  I t was  CHIRAL MIXED DIESTERS.  shown i n P a r t I I o f t h i s  pronounced  effect  on  the  t h e s i s t h a t the s o l i d  enantioselectivity  of dibenzobarrelene diesters.H-  rearrangement  active products with exceptionally high preted  as  an  indication  III,  concluded be  from  to  above r e s u l t s the  Figure  from by one  of the  decided  to  in principle,  between  s i d e s of the v i n y l  double  alternative vinyl  d i s c r i m i n a t i o n .  1  1  d  carbons  s t a t e may  i n f l u e n c e the  so  reaction  occurs  four  the  alternative  reaction  In  can  • Acombination  t h a t the s o l i d that  bond.  mixed d i e s t e r s ,  we  also of  the  selectivity  preferentially  pathways  by  presented  in  a n a l y z e an e x p e r i m e n t a l model t h a t w o u l d a l l o w u s , to determine  the r e l a t i v e  amounts o f p r o d u c t s  e a c h o f t h e f o u r r e a c t i o n p a t h w a y s . S u c h a m o d e l c o u l d be  d i b e n z o b a r r e l e n e d i e s t e r s p o s s e s s i n g two of  paths A-I B-I  yields  73.  We least  enantiomeric  optically  o f a s u b s t a n t i a l degree of s e l e c t i v i t y  significant  rearrangement  f o l l o w i n g one  formation of  study of a s e r i e s of c r y s t a l l i n e  suggested  di-rr-methane  inter-  t h a t t h e r e a c t i o n a t t h e two  subject  of  the  The  )  the  have a  was  r e a c t i o n pathways at the a l t e r n a t i v e Part  of  s t a t e may  and  which  should  be  chiral.  a n d A - I I w o u l d be  I n F i g u r e 73,  d i f f e r e n t i a t e d from  the  from  pathways  carbons  products  A-I  r e c o g n i z e d as d i a s t e r e o m e r s  and  [ C ( l l ) or C(12)]. A-II,  o f each other.  and  from B-I  At  arising  constituted  substituents,  the products  B - I I as b e i n g r e g i o i s o m e r i c s i n c e t h e y o r i g i n a t e  bridging at different v i n y l products  different alkyl  at  arising from  from paths  from  benzb-vinyl  the  same  and  time,  B - I I , would  be  -177-  COOR* RlOOC  Ri Me Et iPr  R* sBu sBu sBu  Glc  peaks  64A-I 72A-I 741  64A-II 72A-II 7411  A-I  A-II  64B-I 72B-I 751  F i g u r e 7 3 . The D i - j r - M e t h a n e R e a r r a n g e m e n t o f C h i r a l M i x e d  64B-II 72B-II 7511  Diesters.  -178-  S e v e r a l compounds w e r e i n i t i a l l y included and  s y n t h e s i z e d f o r t h i s purpose.  t h e m i x e d d i e s t e r s Me/sBu-31, M e / i P e n - 3 4 , Me/Menth-36, E t / s B u - 3 9  iPr/sBu-42.  However,  due  to  experimental  difficulties  d e t e r m i n a t i o n o f t h e d i a s t e r e o m e r i c p r o d u c t s f r o m compounds Me/Menth-36, t h e s e compounds section.  The  solution  were n o t a n a l y z e d  regioselectivity  d i s c u s s e d i n t h e p r e v i o u s s e c t i o n . The Me/iPen-34  was  photochemistry The  also  included  commercial  there,  of  solid  in  the  these state  along  with  in  Me/iPen-34  context two  of  the and this  compounds  regioselectivity  was of  some  aspects o f the  were  prepared  o f d i e s t e r s Me/sBu-31 a n d E t / s B u - 3 9 .  sec-butyl derivatives (S)-(+)-,  studied i n this  thesis  and (R,S)-sec-butanol.  42 w e r e p r e p a r e d w i t h purpose  These  racemic  o f comparing  and  Crystals  optically  possible differences  pure  i n their  of diesters  materials  with 31  with  and the  s o l i d s t a t e photochem-  istry.  Photochemistry  i n Solution.  The d i e s t e r s Me/sBu-31, E t / s B u - 3 9 a n d i P r / s B u - 4 2 direct tion  irradiation  i n acetone.  resulted  in  i n benzene and a c e t o n i t r i l e Glc  three  analysis  of  the  sec-butyl  peaks,  were independent  i n Table X I I I , i n the cases  of  compounds  by  sensitiza-  containing  compounds  peaks (B, A-I and A - I I ) w i t h r e t e n t i o n times materials.  compositions used  photolyzed  s o l u t i o n s and by  longer than those o f the s t a r t i n g presented  were  slightly  The i n t e g r a t e d a r e a s o f t h e s e o f t h e two e n a n t i o m e r i c  Me/sBu-31  Compound E t / s B u - 3 9 was o n l y s t u d i e d i n i t s o p t i c a l l y p u r e  and form.  iPr/sBu-42.  -179-  Table  XIII.  G l c A n a l y s i s of the Photoproducts o f D i e s t e r s  Me/sBu-31,  Et/sBu-39 and i P r / s B u - 4 2 .  glc Compound (S)-(+)-(31) (R,S)-(31)  c  C  A r e a % ("RT)  peak A - I I  peak B  peak  A-I  4 0 ( 2 1 . 3)  2 7 ( 2 2 . 7)  3 3 ( 2 3 . 2)  4 0 ( 2 1 . 3)  2 7 ( 2 2 .•7)  3 3 ( 2 3 . 2)  d  5 0 ( 1 9 . 9)  2 3 ( 2 0 . 7)  2 7 ( 2 3 ..2)  (S)-(+)-(42)  e  5 6 ( 1 6 . 3)  2 1 ( 1 6 . 6)  2 3 ( 1 6 . .9)  5 6 ( 1 6 . 3)  2 1 ( 1 6 . .6)  2 3 ( 1 6 ,.9)  e  ( a ) C o l u m n : DB-1 (°C):  195,  The  regioisomeric  signals  their  c o u l d be  t i o n was  (b) R e t e n t i o n t i m e  by  and, data  independent  based  information  identity  ( d ) 200,  temperature  (e) 200,  o f the products g i v i n g r i s e NMR  analysis  with  the  the  data  from  synthesis.  authentic  The  12.5.  to the three  i P r / s B u - 4 2 , by  regioselective  presented  10;  Oven  i n the case o f d i e s t e r  on the s t r u c t u r a l  was  10;  (min); (c)  e s t a b l i s h e d by glc-MS and  mixtures  spectroscopic  obtained  15M;  column head p r e s s u r e ( p s i ) :  photolysis  glc-MS  of  i n T a b l e X I I ( p a g e 139) and  f o r the  the  comparing products  identifica-  correlation described i n Part III.  f r o m compounds M e / s B u - 3 1 a n d E t / s B u - 3 9 , for  b  (S)-(+)-(39)  (R,S)-(42)  glc  a  This  photoproducts  i s shown i n T a b l e X I V  (below)  t h e p h o t o p r o d u c t s f r o m compound i P r / s B u - 4 2 . The  mass  spectra  of  the  products  from  compounds  31,  39 a n d  c o r r e s p o n d i n g t o peak B were c o n s i s t e n t w i t h the s t r u c t u r e s e x p e c t e d  42  from  -180-  products  v i a pathways  B-I and B - I I (bonding, i n F i g u r e 73, a t t h e v i n y l  carbon n e x t t o t h e e s t e r groups spectra  were  characterized,  = Me, E t a n d  i n p a r t , by fragments  o f MeOH a n d MeOH + CO, EtOH a n d EtOH + respectively peaks  (Figure  CO,  7 4 ) . The f r a g m e n t  of  the photoproducts  and  indicative  iPrOH  and  identical  t o each  fragments  analysis  does  (Figure  74). I t should  not distinguish  o f the loss iPrOH  +  CO  other,  were  a r i s i n g from pathways A - I and A - I I and  w e r e c h a r a c t e r i z e d b y l o s s o f sBuOH, sBuOH + CO a n d 2 - b u t e n e , specific  The  ions from p r o d u c t s g i v i n g r i s e t o  A - I a n d A - I I , which were e s s e n t i a l l y  indicative  i P r respectively).  between  be  among  other  noted that the present  diastereomeric  products  from  pathways I and I I . COOR COOsBu M  P e a k f3 70eV  M  +  - (ROH)  M  +  - (ROH + CO)  M  -(sBuO ) +  M  - ( s B u O + CO)  COOsBu ROOC  M  Peak A - I COOsBu COOR Peak A - I I  Figure  70eV  M  -(sBuOH)  M  -(sBuOH + CO)  M  -(RO )  M  -(RO + CO)  74. Mass S p e c t r o m e t r i c F r a g m e n t a t i o n o f t h e P h o t o p r o d u c t s  Photolysis o f Sec-butyl containing Dibenzobarrelene Diesters.  from  -181-  Table XIV. Selected  Fragment-ions from Relative  m/e  Intensity  neak B  peak A - I  Deak B - I I  15  10  9  -  334  0  7  10  C H  330  9  0  0  iPrOH  316  0  11  12  sBuOH  303  4  5  4  i P r O H + CO  302  14  2  1  iPrO-  289  23  4  5 '  sBuOH + CO  288  6  19  22  247  100  100  100  C  8 16°2  202  80  73  70  C  12 16°4  390(M+)  The r e g i o i s o m e r i c the  Photoproducts of D i e s t e r 42.  Fragment  4  8  glc-MS peak a s s i g n m e n t s were  further  H  H  supported  c a s e o f t h e p h o t o l y s i s p r o d u c t s f r o m d i e s t e r i P r / s B u - 4 2 when  method.  regioisomeric sec-butyl  These  p u r i t y by g l c )  were  from  synthesized -  the  1  isopropyl  m o n o a c i d 41 r e s p e c t i v e l y ( F i g u r e  these preparations the  compounds  isopropyl  3 2  i n two monoacid  X-ray characterized dibenzosemibullvalene  by the  steps (90% 40  and t h e  a s i m i l a r procedure  41 i s c o n v e r t e d i n t o t h e p r e v i o u s l y  i n  authentic  7 5 ) . The r e g i o s e l e c t i v i t y  c o u l d be e s t a b l i s h e d b y u s i n g  monoacid  + CO  sBuO- + CO  s a m p l e s o f compounds 7 5 I / 7 5 I I a n d compounds 7 4 I / 7 4 I I w e r e a n a l y z e d same  lost  from where  i s o l a t e d and  6 3 A by treatment with  methanol.  -182-  HOOC  ,  C  0  0  i  P  COOiPr  r  * COOiPr sBuOOC I  I COOsBu 1)  hv  2) C2O2CI2 75(1/11)  3) sBuOH  COOsBu*  COOsBu*  iPrOOC I  I COOiPr  1)  hv  2) C2O2CI2 74(1/11)  3) iPrOH  75.  Figure 75I/75II  and  The as we  Regioselective  above,  diastereoselectivity  arising  C o n t r a s t i n g l y , products a r i s i n g  single  peak (peak B), and t h e i r r e l a t i v e  same  75I/75II to  methodology.  With a u t h e n t i c  and  quantify  from pathways B-I and B-II g i v e amounts cannot be samples  their relative  m i x t u r e o f the s t a r t i n g m a t e r i a l of  NMR  and o f the samples several  (peaks A-I v e r s u s peaks  determined  o f the r e g i o i s o m e r i c  i n hand, i t became d e s i r a b l e to develop an a n a l y t i c a l  resolve  series  Dibenzosemibullvalenes  from pathways A-I and A - I I ,  can be determined by g l c a n a l y s i s  A-II).  the  of  74I/74II.  relative  saw  Preparation  solvents.  by  pair  method a b l e  amounts i n the t o t a l  iPr/sBu-42.  a  With t h i s , purpose  photolysis i n mind, a  s p e c t r a o f the t o t a l p h o t o l y s i s m i x t u r e from compound 4 2 containing The  goal  74I/74II  and  of  study was  this  75I/75II  were  explored  to f i n d an i d e a l l y  in well  -183-  resolved signal relative  from each photoproduct  diastereomeric  f o r the purpose  r a t i o s by  NMR  integration.  t h e b e s t r e s o l u t i o n came f r o m t h e s i g n a l s o f H ( 8 d ) XV  f o r numbering),  of  s i n c e t h e s e were s h a r p s i n g l e t s  assigning  I t was  found  (see formula isolated  in  The c h e m i c a l s h i f t s  signals  and  included i n Table  to  these  hydrogens  of  that Table  from the r e s t  of the dibenzosemibullvalene d i e s t e r s i g n a l s . corresponding  the  those  of  the  a t C(4b) are  XV.  E  5  T a b l e XV. The Diester  i  H  NMR  Resonances  H  of  H(8d)  4  and  H(4b)  from  Products  i P r / s B u - 4 2 as a F u n c t i o n o f Four D i f f e r e n t S o l v e n t s .  Solvent-d  5H8d(No.  o f H)  H4b(No.  o f H)  Acetone  4.35(1), 4.37(2),  4.39(1)  5.06(2),  5.08(2)  Acetonitrile  4.38(1), 4.39(2),  4. 4 1 ( 1 )  5.06(4)  Chloroform  4.41(1),  4.42(3)  5.03-5.01(4)  Benzene  4.76(1).  4.77(3)  5.10(2).  5.12m.  5.14(1)  of  -184-  Th e  best  signals  of 75I/75II a t 6 4.37  74I/74II one  resolution  of the  relative  two  of  H(8d)  a p p e a r e d a t S 4.35 and  4.39  diastereomers  and  o f 75 was  (normalized with respect  products)  by  s u b t r a c t i n g the  4.37  i n a c e t o n e - d g where and  the  to  signals  pathways  B-I  a  of  total  751  or 7511),  and  B-II  100%  of  regioselectivity  information  in  the  case  of  the  of d i e s t e r  s h o u l d be  p o i n t e d out  t h a t the a b s o l u t e s t e r e o c h e m i s t r y o f the  C(4b),  C(8b),  information up  t o now,  Table  [given C(8c)  and  by  and  XVI.  four c h i r a l  C(8d)],  cannot  H  l  751  56° 27  b  Combined  a)  Estimated  from  error +5  I n t e g r a t i o n (%) 741  ---  21  29  %; b )  from D i e s t e r  7511  ---  27  c) S i g n a l s not  (as  from  XVI.  7411  23  49 d  Estimated  24 21  e r r o r ± 10  r e s o l v e d ; d) C a l c u l a t e d v a l u e .  23  %;  It  diastereom-  the  carbons present pairs,  illustrative.  a  NMR  deduced  R e l a t i v e Y i e l d s of Photoproducts  Analysis:  i n Table  dibenzosemibullvalene  be  be four  ppm  assignments between d i a s t e r e o m e r i c  Photoproduct  glc  i s presented  the  the s t r u c t u r a l  remains only  the  products  photolysis  products  the  ( a l s o as p e r c e n t ) .  solution  eric  iPr/sBu-42  from  can  i n t e g r a t i o n f r o m t h e s i g n a l a t 4.35  from the glc-determined  the of  Even though o n l y the s i g n a l  resolved (either  between  calculated  A summary o f t h i s  obtained  respectively.  diastereoselectivity  percent)  was  iPr/sBu-42.  -185-  The  r e s u l t s shown  iPr/sBu-42  follows  benzo-vinyl  bridging  ent  i s attached.  E t / s B u - 3 9 , on bond  The  the  formation  substituent. compound  is  Tables  a  reaction  at  XII  the v i n y l  case of the  the  vinyl  and  which  i P r / s B u - 4 2 . The ^5%,  d e p e n d i n g on  the  from a given  compound.  A  small  A-I:peak  the  containing  ~  carbon  may  results  be  45:55,  and  This of  a  due noted  error  the  sample o b t a i n e d  the  substitu-  to the  the  to  of  also  sec-butyl  1 0 2  influence  isopropyl  the  i n a l l our  was  pathways  f o u n d t o be  31,  be  slightly  and  A-II  39  and  42  case of  the 741  a  supported  when  Figure  diazomethane  o f d i b e n z o s e m i b u l l v a l e n e Me/Me-52 (two  73  of  was (peak  isopropyl and  7411 These  significant  the  of  page  the  photolysis  i n p a g e 177)  (see  the  larger  A-I  impose  our  observed  the v i n y l - f a c e s e l e c t i v i t y  i n t h i s manner p r e s e n t e d a s m a l l  is  i n a s i m i l a r range.  group does n o t  reaction with  in  regioisomeric  photoproducts  above). I n the  further  III)  containing error  glc  and  sec-butyl  determinations  h o w e v e r , may  compounds  on  Part  bulkier  a systematic  that  ( f o u r d i a s t e r e o m e r s , see and  (see  s e l e c t i v i t y between products  was  conclusion  (S)-(+)-42  sample  by  h e a v i l y based, i s poorer i n  errors,  Table X I I I  B-II  submitted to h y d r o l y s i s give  statistical  systematic  stereo-differentiating  mixture  attached  r e s u l t s are  glc determination  indicate that  reaction.  our  compound ( 4 2 ) ,  f r o m pathways B-I  compound  reaction  isopropyl  normally observed  d i a s t e r e o s e l e c t i v i t y between  A-II  involves  a n a l y t i c a l r e s o l u t i o n between the  observed from the  that  r e g i o s e l e c t i v i t y o b s e r v e d f o r compounds M e / s B u - 3 1  unexpected  of  indicate  that  d i f f e r e n t r e g i o s e l e c t i v i t yof  upon  order  XVI  carbon to which the  a n a l y t i c a l m e t h o d o l o g y . I t s h o u l d be resolution,  and  pathway  o t h e r hand, f a v o r s at  The  in  203)  enantiomers).  o p t i c a l r o t a t i o n ([a]n  was to The =  -186-  0.24°),  which  reflects  on t h e f a c e s e l e c t i v i t y 741  and  the disymmetric induction o f the sec-butyl o f the rearrangement  7 5 1 , a n d t h e o t h e r from 7411 and 7511).  o f 52 c a l c u l a t e d o f f r o m t h i s with  ( o n e e n a n t i o m e r o f 52  the  diastereomeric  handle from  The e n a n t i o m e r i c e x c e s s  t r e a t m e n t ( e . e . = 1.5±0.5%) c o r r e l a t e s  excess  1 0 2  well  o f 74 a n d 75 c a l c u l a t e d b y g l c a n d  NMR:  [(7411 + 7511) - (741 + 7 5 1 ) ] d.e.  =  x 100 =  2%  [(7411 + 7511) + (751 + 7 5 1 ) ]  Studies  The the  i n the Solid  solid  packing  State.  state reactivity, arrangement  a s we h a v e s e e n , d e p e n d s s u b s t a n t i a l l y  present i n the c r y s t a l  lattice.  The c r y s t a l l i z a -  t i o n b e h a v i o r o f compounds h a v i n g p e r m a n e n t m o l e c u l a r  chirality  some  briefly  particular  facilitate  they  of Chiral  present  lattice  necessarily  as  pack  unspecified  the  be  reviewed  state photochemical  enantiomers  enantiomer  space g r o u p s .  i s a n e q u i m o l a r m i x t u r e o f t h e two state,  7 8  have  been  on  whether  o r as t h e racemate.  i n one o f t h e 65 e n a n t i o m o r p h o u s  physical  i n order to  results.  compounds d e p e n d s p r i m a r i l y  pure  presents  9 3  i s b u i l t up w i t h m o l e c u l e s o f a p u r e  of t h e racemate, which an  will  Compounds.  crystallization of chiral  are  crystal  which  the discussion o f the s o l i d  Crystallization  The  features  on  found  to  When a  i t will 9 4  Samples  enantiomers present  in  three  -187-  different  crystallization alternatives.  5  1) A r a c e m i c m o d i f i c a t i o n o r r a c e m i c compound, single  crystalline  phase  composed  of  equimolar  e n a n t i o m e r s , o b v i o u s l y w i t h a racemic space 2) C r y s t a l l i z a t i o n b y s p o n t a n e o u s crystallizes  as  enantiomorphous are  a  heterogeneous  p h a s e s . The  Crystallization  composed o f  either  variable  in a solid amounts  those o f the c h i r a l  The  of c h i r a l  r e s u l t i n g from  of  the  realized  two  a two  racemate two  crystallizations  or o f the racemic  whose  properties  fundamental  types  of  Additional t h a n one  complications  to  the phase  be  in  a  that can  be  modifications.  types of c r y s t a l l i n e  may  t h a t can  usually  and c r y s t a l p r o p e r t i e s  by c o n s i d e r i n g a b i n a r y system  crystallization)  i s a phase  enantiomers,  (ternary be  racemates  i f solvent  described  enantiomeric  proposed a c c o r d i n g t o t h e i r m e l t i n g p o i n t diagrams  by  mixtures  can  i s needed the  phase  have been  a s shown i n F i g u r e  d i a g r a m c a n be  76.  e x p e c t e d when more  c r y s t a l l i z a t i o n b e h a v i o r o c c u r s a t t h e same t i m e ; t h e s e w i l l  not  discused here. In  the  phase  diagrams  i n F i g u r e 76 t h e v e r t i c a l  equilibrium  t e m p e r a t u r e o f t h e sample  and t h e  the  c o m p o s i t i o n f r o m 100%  enantiomer,  the  the  c r y s t a l s o f the  such  s o l u t i o n , which  i d e n t i f i c a t i o n of the d i f f e r e n t  r u l e . T h r e e  be  of  r e s o l u t i o n r e s u l t s when t h e  d i s o r d e r e d manner and w i t h space groups  in  amounts  of  a l s o r e f e r r e d t o as r a c e m i c m i x t u r e s o r c o n g l o m e r a t e s . 3)  be  consists  group.  mixture  samples  which  sample  phase  diagrams  dotted lines,  horizontal  axes  represent to  100%  are three regions i n  the  d e p e n d i n g on t h e phases p r e s e n t . A t t e m p e r a t u r e s b e l o w  the  o p p o s i t e enantiomer,  or solidus  (-)  one  axes r e p r e s e n t the  to the r i g h t .  lines,  only  There  solid  (+) t o t h e l e f t ,  phases  can  coexist  under  -188-  equilibrium  c o n d i t i o n s . Above  the f i l l e d ,  homogeneous l i q u i d phase c a n e x i s t . regions coexist  is  the  region  of  The  or l i q u i d u s l i n e s ,  space  between  t h e phase d i a g r a m where  the solid  only a single two  previous  and l i q u i d  can  i n equilibrium.  (b)  (+ )  (-)  (+) Figure  III.  Type  II  Mixture,  (b)  the  (c) S o l i d S o l u t i o n s (Mixed C r y s t a l ) o f the Enantiom-  ( I ) I d e a l o r R o o z e b oom  Roozeboom  (-)  76. B i n a r y P h a s e D i a g r a m o f ( a ) t h e R a c e m i c  R a c e m i c Compound a n d , ers:  (-)  (+)  and  Type 1,  ( I I ) Non-Ideal  with  a  Maximum  ( I I I ) N o n - I d e a l w i t h a Minimum o r Roozeboom  ( A d a p t e d f r o m R e f e r e n c e 93)  or Type  -189-  The  b i n a r y phase diagram  characterized  by  phous phases and of  the  the  of  the  racemic  maximum m e l t i n g p o i n t s o f t h e  diagram  composed  is  composed  of  only  one  s o l i d phase i s g i v e n by eutectic  point,  o f two  d i f f e r e n t and  enantiomer  Any  two  and  The  (a),  amounts  of  solid  enantiomorphous  of the  i n e q u i l i b r i u m w i t h a racemic  not  with  the  solid  phase  region  two  solid  i s necessar-  the c o m p o s i t i o n o f the  crystals  is  enantiomor-  t h e amount o f c r y s t a l s o f e a c h e n a n t i o m e r .  equal  mistaken  pure  single crystal  phases are present be  diagram  a lower m e l t i n g p o i n t o f the e u t e c t i c .  phases a l o n g the e n t i r e c o m p o s i t i o n range. ily  mixture,  entire At  the  enantiomorphous  l i q u i d phase  corresponding  to  and  should  the  racemic  compound. The  typical  Figure  76(b)  phase diagram and  may  m o d i f i c a t i o n possesses the  pure  racemic ers  cases  are  in  compound  These  d i a g r a m s a r e c h a r a c t e r i z e d by of  of enantiomorphous c r y s t a l s  i n e q u i l i b r i u m w i t h the l i q u i d of a s o l i d  (assuming  represented  s h a p e d e p e n d i n g on w h e t h e r t h e  the sample i s composed o f a m i x t u r e  the case  is  a higher or a lower m e l t i n g p o i n t w i t h  m o d i f i c a t i o n and  which In  vary  enantiomers.  p o i n t s at which  of the racemic  solution  unlimited  of  the  solubility)  solution  of  the  sample  (Figure  (Roozeboom t y p e  maintained  constant  classification  I),  along  is the  o f t h e o t h e r two  on w h e t h e r t h e m e l t i n g p o i n t s ,  one  in  entire  of  of the pure  the  enantiom-  phase. enantiomers  have been found  76(c)).  to  eutectic  crystals  three  The  first  which  case,  the  enantiomeric  types of non-ideal s o l i d  limiting  d e p e n d i n g on  v a r i a t i o n o f the m e l t i n g p o i n t w i t h the c o m p o s i t i o n g i v e n by purity  racemic  respect two  in  the an  melting  the  optical  ideal  solid  point  composition. solutions  is The  depends  t h a t v a r y w i t h the sample c o m p o s i t i o n ,  have  -190-  e i t h e r a maximum ( R o o z e b o o m t y p e I I ) o r a minimum The  solid  r e g i o n o f the phase diagrams  of s o l i d  (Roozeboom  solutions  type I I I ) .  i s determined  by  a s i n g l e homogeneous s o l i d p h a s e a l o n g t h e e n t i r e c o m p o s i t i o n r a n g e . 1 3 The  melting points (of single c r y s t a l s ) ,  solid  NMR  s p e c t r a of the racemic m i x t u r e are always  pure  enantiomers  racemic  and  different,  compound a n d  the s o l i d  at least  state  3  to those from  the  from those from  the  t h e m e l t i n g p o i n t s o f two  different  i f they have d i f f e r e n t e n a n t i o m e r i c c o m p o s i t i o n . S i n g l e (enantiomorphous)  LJ  I n the case o f n o n - i d e a l s o l i d  solutions  of the racemic mixture  single  • C  identical  in principle,  solution.^  i n f r a r e d and  crystals  should  normally  be  crystals  a n d o f t h e r a c e m i c compound  will  a l w a y s have f i x e d c o m p o s i t i o n and m e l t i n g p o i n t s . It  has been o b s e r v e d  t h a t the racemic m o d i f i c a t i o n i s by  common c r y s t a l l i z a t i o n a l t e r n a t i v e  adopted by  amounts  However, the o c c u r r e n c e o f  o f t h e two  enantiomers.  resolutions  and o f s o l i d  have  been  also  suggested^  3  thermodynamically 0.2  the  unstable  with  the  time  mixture  of  Pasteur.  (spontaneous  closer  enantiomers  crystals,  It  has  been  resolution)  is  r e s p e c t to the racemic m o d i f i c a t i o n s  (D)-Crystal  — >  a l s o been suggested  by  relationship:  R a c e m i c compound  t h a t the reason f o r t h i s d i f f e r e n c e r e s u l t s  intermolecular packing possible  compound. l-'O I t h a s  same  spontaneous  or mixed  to 2 K c a l / m o l a c c o r d i n g to the f o l l o w i n g thermodynamic  I t has been proposed  pure  since  racemic  (L)-Crystal +  the  samples c o n t a i n i n g the  s o l u t i o n s of the enantiomers,  documented  that  J  f a r the most  i n the c r y s t a l s o f the  t h a t the c r y s t a l  a n d o f t h e r a c e m i c compound may  from  racemic  structures of  the  exhibit significant  one  -191-  o r two  dimensional s i m i l a r i t i e s  f r e q u e n t l y be proposed  and  t h a t the c r y s t a l  deduced from t h a t o f the o t h e r .  t h a t the packing of c h i r a l  molecules arrange f i r s t by  and  1 5 0  common o f  a l l the  compounds. t h e two  or  mixed  m o d i f i c a t i o n and  by  homochiral  compound.  alternatives  for  then  repeat  mirror 1 5 0 0  c r y s t a l s of the enantiomers  crystallization  may  Pedone and B e n e d e t t i have  i n c o m p a c t l a y e r s o r c o l u m n s w h i c h may  i n v e r s i o n c e n t e r s i n the case of the racemic solutions  o f one  compounds o c c u r s s u c h t h a t  t r a n s l a t i o n i n the enantiomorphous  Solid  structure  planes  .  are the  optically  least active  T h i s s i t u a t i o n h a s b e e n f o u n d t o o c c u r when t h e s t r u c t u r e s  9 3  enantiomers  a r e so s i m i l a r  t h a t they can occupy  of  the l a t t i c e  space  Large molecules w i t h a s m a l l  chiral  1 3  of  each  handle  other i n the s o l i d  c a n be  In  site  some  cases  the  two  Optically  pure  of  elements  enantiomers  the  samples  of  o p t i c a l l y pure  the  of  one  until  enantiomer the  and  crystal  racemate  enantiomers.  can  The  of  f i t t h e same  crystal  such  as  typical  of  the  pack  in  s i t u a t i o n can  r e p l a c i n g them b y m o l e c u l e s o f t h e becomes  optically  a  3  sometimes  former  the  t a k i n g out o f a racemic c r y s t a l  the  other  symmetry  p r e s e n t i n t h e o r i g i n a l c r y s t a l a r e t r a n s f o r m e d so t h a t  inversion  g l i d e p l a n e s c a n no  becomes  two  chiral  asymmetric  with  unit.  racemate  by  Independent  pure.  be  The  c e n t e r s and m i r r o r and  the  solutions  (conformational isomorphism).-  m e n t a l l y c o n s t r u c t e d by h y p o t h e t i c a l l y  enantiomer  solid  samples can sometimes pack i n c r y s t a l s  r a c e m i c compound a n d  molecules  of  a t t h e e x p e n s e o f some m i n o r m o l e c u l a r a d j u s t m e n t  s m a l l c o n f o r m a t i o n a l change  crystals  J  good c a n d i d a t e s f o r f o r m a t i o n  enantiomers. lattice  state.  l o n g e r o p e r a t e and  the  crystal  (quasienantiomeric) molecules  C r y s t a l s o f the c h i r a l m o d i f i c a t i o n can  be  built  f o l l o w i n g a s i m i l a r p r o c e d u r e where 50% o f t h e  per with  molecules  -192-  of the c h i r a l Solid  c r y s t a l a r e exchanged by molecules  s o l u t i o n s o f the enantiomers  chiral lattice  r e c o g n i t i o n between the  Solid,  solutions  of  enantiomer.  c a n be c o n s i d e r e d t o r e s u l t  chiral  and the c h i r a l molecular  of the other  molecular  space  structure that w i l l  the enantiomers  can occur  i n  occupy  from a poor the  it.^  crystal  2  i n three general  types 93  a c c o r d i n g t o t h e manner i n w h i c h t h e e n a n t i o m e r i c 1) C r y s t a l l i z a t i o n enantiomers Statistical  i n a d i s o r d e r e d s o l u t i o n r e s u l t s when  i s r e p l a c e d by the other distributions  i na totally  o f the enantiomers  occupancy o f the neighboring  R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R  occur  (S) -  Crystallization  when s u b s t i t u t i o n o f macroscopically largely  i n solid  one  random  one  J  o f the  r a n d o m way ( F i g u r e 7 7 ) . independently  o f the  sites.  >  R S R S R R S R S R R R R S R R R S S R R S R R R R R R R S R R S R S R R S R . R S R R S R  F i g u r e 77. S o l i d S o l u t i o n w i t h S t a t i s t i c a l  2)  exchanges take p l a c e .  Disorder.  s o l u t i o n s with short-range  enantiomer  by  the  other  takes  order  occurs  place  in a  way b u t t h e o c c u p a n c y o f t h e n e i g h b o r i n g s i t e s i s  i n f l u e n c e d by each e n a n t i o m e r i c  molecule  (Figure 78).  -193-  R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R  F i g u r e 78. S o l i d  >  S o l u t i o n w i t h S h o r t Range  3) C r y s t a l l i z a t i o n  i nsolid  solutions  s y m m e t r y o r d e r o c c u r s when m o l e c u l e s two  non-equivalent sites  of  these  manner  two s i t e s  where  enantiomer  one  i n the mixed c r y s t a l  occupies  i n v e r s i o n c e n t e r may a p p e a r racemate  F i g u r e 79. S o l i d  has  been  non-statistical  inverse  crystal  then occurs  occupies  R'-sites.  lattice.  Under  to  the  i na  R-sites  The  occupy  occupancy  non-statistical and  the  other  these circumstances a r e a l crystal  structure  o f the  the  R S R S R S R S R R S R S R S R S R R S R S R S R S R R S R S R S R S R R S R S R S R S R  (S)  >  Solution with Non-Statistical  I n v e r s e Symmetry  p o i n t e d o u t t h a t t h e most i m p o r t a n t r e q u i r e m e n t  formation o f a s o l i d between  with  (Figure 79).  R R'R R'R R'R R'R R R'R R'R R'R R'R R R'R R'R R'R R'R R R'R R'R R'R R'R R R'R R'R R'R R'R  It  always  leading  Order.  i n the enantiomorphous c r y s t a l  R a n d R' i n t h e i r  enantiomer  always  R R S S S R R R R R S S S S R R R R R R S S S R R R S R S R R R R S S S R S S S R R S S S  (S)  solution  compounds  refers  forming  a  to  the  mixed  requirement  i s also determining i n the  structures  and i t has been observed  size  and  crystal.  formation  1 3  of  shape  Order.  f o r the  similarity  Interestingly, isomorphic  that isomorphic c r y s t a l s  of  this  crystal different  -194-  compounds c a n o f t e n f o r m c o n t i n u o u s proposed  an  solid  solutions.  Kitaigorodsky  has  e m p i r i c a l and s e m i q u a n t i t a t i v e e s t i m a t e o f t h e l i k e l i h o o d  of  1o two  compounds f o r m i n g a s o l i d  This  estimate  similarity  be  obtained  e t h a t r e s u l t s from  overlapping  volumes  molecular f i t cally  can  s o l u t i o n or isomorphic c r y s t a l  of  from  the  coefficient  structures.  of  geometrical  the r a t i o between the n o n - o v e r l a p p i n g  the  compounds  h a s b e e n o b t a i n e d . The  under  comparison a f t e r  coefficient  £ is  J  defined  and  the best  mathemati-  a c c o r d i n g t o the f o l l o w i n g f o r m u l a :  e = 1 - ( n o n - o v e r l a p p i n g volume) / ( o v e r l a p p i n g  The  closer  look a l i k e  and  isomorphism.  of e to unity  the  value  the  larger  Although  r e q u i r e s the knowledge  a  the  volume)  t h e more t h e two m o l e c u l e s  probability  of  solid  solubility  p r o p e r e s t i m a t e o f the m o l e c u l a r volume  of the c o n f o r m a t i o n  of  the  two  based  on  d e v i s e d by  a group  increment approach.  a r e c o n s i d e r e d t o be defined  Kitaigorodsky  formed  by  1 3 , 3  ^  and  tabulated methodology structural  a  Waals  number  radii. of  smaller  radicals  Gavezzotti  u s e f u l group  1 4 4  has  or  A s i m p l e and  Bondi ^ 1  which  1  groups  d e f i n e d by recently  increments deduced  t o c a l c u l a t e a t o m i c and m o l e c u l a r volumes parameters.  under  is  I n t h i s approximation the molecules  by o v e r l a p p i n g atomic spheres w i t h volumes  d e r i v e d van der  and  usually  molecules  c o m p a r i s o n , a p p r o x i m a t e m e a s u r e m e n t s c a n s o m e t i m e s be u s e f u l . u s e f u l m e t h o d was  will  which their updated  from an  from X-ray  are X-ray and  improved measured  -195-  The  S o l i d State  Properties  The  state  solid  iPr/sBu-42 w i l l could  be  the  solid  properties  be d i s c u s s e d  obtained  information  and P h o t o c h e m i s t r y o f D i e s t e r 42.  photochemical  since  partial  results f o r diester  X-ray  f o r t h e two c r y s t a l l i n e m a t e r i a l s .  obtained  f o r m t h e s e compounds w i l l  structural 1 5 2  be u s e f u l  The r e s u l t s a n d i n  o f d i e s t e r i P r / s B u - 4 2 were grown f r o m t h e m e l t ,  and  f r o m many o t h e r s o l v e n t s  by  using  ( d i e t h y l ether,  acetonitrile,  o p t i c a l l y pure and racemic m a t e r i a l s .  p h i s m was o b t a i n e d The  from m a t e r i a l s  melting  point  m a t e r i a l was 11° h i g h e r (122-4°C).  interpreting  The  of  crystals  (133-5°) t h a n t h e m e l t i n g  difference  i n melting  points,  crystalline  ethanol  hexane,  etc.)  No i n d i c a t i o n o f p o l y m o r -  analyzed by s o l i d single  from  state of  FTIR  spectro-  the o p t i c a l l y  point  of  the  pure  racemate  i n d i c a t i v e o f two d i f f e r e n t  c r y s t a l phases, and the l a c k o f o p t i c a l r o t a t i o n from s o l u t i o n s single  data  s t a t e p h o t o c h e m i s t r y o f compounds M e / s B u - 3 1 a n d E t / s B u - 3 9 .  Crystals  scopy.  first  and  of several  samples o f t h e racemate, e x c l u d e d the p o s s i b i l i t y  of a  spontaneous r e s o l u t i o n i n t o c r y s t a l s o f t h e pure e n a n t i o m e r s . A few s i n g l e crystals of  grown from t h e racemate i n d i c a t e d a s m a l l  state  identical similar  infrared  the  s p e c t r u m o f t h e o p t i c a l l y p u r e m a t e r i a l was  t o the spectrum from c r y s t a l s o f solid  phase  FTIR s p e c t r a  almost of  enrichment  10% o r l e s s w i t h o u t a n y p r e f e r e n c e f o r e i t h e r o f t h e two a n t i p o d e s . The  solid  The  enantiomeric  identical  of a solid  the  racemate  of  the  t o those o f c r y s t a l s o f the c h i r a l  diisopropyl  diester  23  suggesting  s o l u t i o n o f the enantiomers  and the c r y s t a l morphology  (Figure  isomorphic c r y s t a l structure r e l a t i o n s h i p .  38,  Part  two  almost  (Figure  materials  P2^2^2^  the 80). were  modification  I I ) suggesting  an  ¥  Figure Diester  80.  Solid  iPr/sBu-42:  State  FT-IR S p e c t r a o f C h i r a l  (a) Racemic and (b) O p t i c a l l y  P2 2 2  Active.  1  1  1  Crystals  of  -197-  Our  empirical  conclusions  generation of optically material  but  also  were  supported  by  the  a c t i v e p r o d u c t s not o n l y from the  from  the  racemate.  photochemical  optically  The i s o m o r p h i s m was  pure  definitely  c o n f i r m e d when s i n g l e c r y s t a l X - r a y d i f f r a c t i o n a n a l y s e s w e r e p e r f o r m e d o n crystalline ing  samples o f t h e o p t i c a l l y pure and r a c e m i c m a t e r i a l s .  e v i d e n c e was  P2^2i2i, samples  but  found not only i n the e x p e c t e d l y i d e n t i c a l  a l s o on t h e l a t t i c e  Convinc-  space  parameters o f the c r y s t a l s  groups,  of the three  (Table XVII).  F u r t h e r r e s e m b l a n c e b e t w e e n t h e a b o v e c r y s t a l l i n e m a t e r i a l s was i n t h e i r X-ray molecular structures. characteristic structure  of  carbonyl-vinyl  structural the  T h i s c a n be d o c u m e n t e d f r o m t h e m o s t  parameters  used  to  d i b e n z o b a r r e l e n e compounds  t o r s i o n angles presented  disymmetry  conferred  essentially  identical  by  the  in  compounds.  describe  studied  Table  conformation  f o r a l l three  'found  the  i n this  XVIII.  The  molecular thesis,  the  molecular  of the ene-dioate system  was  -198-  Table XVII.  L a t t i c e Parameters o f P2i2^2^ C r y s t a l s o f  Compounds  23,  (S)-(+)-42 and (R,S)-42. iPr/iPr-23  iPr/(S)-(+)-sBu-42  iPr/(R,S)-sBu-42  a(A)  8.3304  8.4936  8.4624  b(A)  11.6893  11.9210  11.8705  c(A)  21.7937  21.6691  21.6788  a=fi=T)  (degrees)  Space group  90  P2^2^2^  Z (A )  Density  3  (g/cm ) J  90  P2 2 2 1  1  1  P2 2 2 1  1  1  4  4  2122.20  2194.14  2177.70  1.1767  1.1381  1.1467  4  Volume  90  (a) C a l c u l a t e d d e n s i t y .  -199-  Table  XVIII.  (S)-(+)-42  and  Conformation  of  the Ene-dioate System i n D i e s t e r s  23,  (R,S)-42. (CH3) (CH3)  •  Torsion  Diiso-23  Angle  63.7  68.4  70.1  0(4)-C(17)-C(12)-C(ll)  164.3  166.2  167.4  c o n f o r m a t i o n o f the e n e - d i o a t e chromophore g i v e s the d i b e n z o b a r r e -  lene s t r u c t u r e a m o l e c u l a r disymmetry  in  (R,S)-42  0(2)-C(13)-C(ll)-C(12)  The  of  (S)-(+)-42  the s e c - b u t y l group  t h a t i s independent  substituent. A single  a n o n - s e l e c t i v e manner b y m o l e c u l e s  case o f the racemate. elucidated  The  of  X-ray molecular s t r u c t u r e ,  or  diester  42  resulted  was  that  both  i n the  structures  disordered solid  the  a c t i v e and  s o l u t i o n of the  occupied  ( R ) - ( - ) - 4 2 i n the not  correspond  fully  disorder, revealed of  the  o f the i s o p r o p y l  diisopropyl  may  c a n be  structures  replacement  present i n both the o p t i c a l l y  thus suggesting statistically  from  in  chirality  although  as a r e s u l t o f s u b s t a n t i a l c r y s t a l l o g r a p h i c  a t t a c h e d t o the a l k o x y oxygen 0(1) disorder  site  of (S)-(+)-42  t h a t the l o c a t i o n o f the s e c - b u t y l group forms  lattice  o f the  diester  23.  two group This  racemic  materials,  to  non-ideal  enantiomers.  a  -200-  Further enantiomers points  from  evidence  for  o f compound single  the  42 was  crystals  mutual obtained grown  solid  state  solubility  of  by  observing  different  from  solutions  p r e p a r e d by m i x i n g  amounts o f t h e o p t i c a l l y p u r e  Although  t h e e x a c t c o m p o s i t i o n i n t h e s o l i d p h a s e was n o t d e t e r m i n e d , are  strongly  indicative  and r a c e m i c m a t e r i a l s  melting  different  measurements  the  of  a  non-ideal  (Table X I X ) .  solid  our  solution  ( R o o z e b o o m t y p e I I I ) w i t h a minimum m e l t i n g p o i n t .  Table XIX. M e l t i n g P o i n t s of Mixed  mole % (S)-(+)-42  The  i n solution  of Diester  42.  melting point  50  122-4  60  126-8  70  129-31  80  131-2  90  132-4  100  133-5  (°C)  r e l a t i v e yields of a l l four possible diastereomeric products  determined by the solution  Crystals  NMR  photolysis  and g l c methodology d e v e l o p e d  (Table  XV, p a g e 1 8 3 ) .  i n the case o f  The p r o d u c t d i s t r i b u t i o n  f o u n d t o b e s u b s t a n t i a l l y d i f f e r e n t when p h o t o l y s e s w e r e the o p t i c a l l y pure  and racemic c r y s t a l l i n e  materials.  carried  out  were the was in  -201-  Table  XX. S o l i d S t a t e S t e r e o s e l e c t i v i t y  Compound iPr/(+)-sBu-42  D  iPr/(±)-sBu-42  a) NMR  z  751  b  f r o m Compound 4 2 . a  74II(%)  85  5  5  5  31  31  8  31  S t r u c t u r e s shown i n F i g u r e 8 3 , p a g e 2 0 6 ; b ) V a l u e s  determined  by  L  H  and g l c .  Photochemistry  o f t h e O p t i c a l l y Pure C r y s t a l l i n e  Photolysis of c r y s t a l s of the o p t i c a l l y significant one  z  741  75II(%)  vity  observed  (bonding steric carbon  solid  attached  carbon,  hypothesis  i n the isomorphic  regioselecti-  C(ll),  which  is  is  next  to  carboxylate  consistent  with  p r e d i c t e d b o n d i n g a t t h e same  diisopropyl derivative  stereochemistry  r e q u i r e s knowledge o f centers, skeleton  C(4b),  82,  the  C(8b),  (see Table  in  Figure  and  the {(R)-C(4a),  of  the  absolute  C(8c)  and  XV f o r n u m b e r i n g ) .  generate  respective  (R)-C(8c),  group our vinyl  of  the  the  structures asymmetric  i n the dibenzosemibullvalene  P a t h w a y s 12-1 a n d 1 2 - 1 1 , a s  the {(S)-C(4a),  (R)-C(8b),  photoproduct  stereochemistry C(8d),  the  (page 1 7 2 ) .  D i s t i n c t i o n b e t w e e n p a t h w a y s 12-1 and 12-11 a n d t h e a s s i g n m e n t o f absolute  a  of a preference f o r  to the 0(1)-C(13)-0(2)  that  in  ( 9 0 % , T a b l e XX) b e n z o - v i n y l  12-1 and 12-11, F i g u r e 8 2 ) . T h i s r e s u l t compression  resulted  s t a t e r e a c t i o n p a t h w a y s . The  a t the v i n y l  substituent  sample  indicative  i n d i c a t e s t h a t t h e more f a v o r e d  bonding step occurs isopropyl  pure  r e g i o - and d i a s t e r e o s e l e c t i v i t y  o f the four a v a i l a b l e  Material.  (S)-C(8b),  (S)-C(8c),  shown  (S)-C(8d)}  (R)-C(8d)}-dibenzosemibullvalene  -202-  stereochemistry the  solid  specific  respectively.  state mixture  s i n c e we know  the absolute  rotation  t h e analogous  diisopropyl  of  diester all-(S)-(-)-57, between  This assignment i s p o s s i b l e i n t h e case o f  this  a n d we c a n p e r f o r m  compound  stereochemistry  dibenzosemibullvalene  a stereochemical  and the major photoproduct  and  correlation  ((+)-75I)  from  7 8  diester  (S)-(+)-42. A direct polarimetric  comparison  r o t a t i o n o f t h e photoproducts  would  from (S)-(+)-42  perhaps obscuring c o n t r i b u t i o n a r i s i n g Ideally, its  i n order  optical  the  the  pure  the major photoproduct dibenzosemibullvalene  the homologation  total  He/He-.  solid  52.  process..  s t a t e photoproduct  The  absolute  mixture  the o p t i c a l  {[Q]  d  •=  and  activity  The p u r e s o l i d 20.6°,  sis  active  dimethyl  their  mixture  absolute reasons  into the  (c=0.3,  CHCI3)}  stereochemistry we h a v e  converted  dibenzosemibullvalene  d e d u c e d i n t h i s manner s h o u l d b e 85% o f t h e  mixture  total  dominate  mixture. from  O.llOg  of  (S)-(+)-42  was o b t a i n e d b y p a r t i a l p h o t o l y s i s a n d  (diazomethane) and s e p a r a t i o n o f  the  were t r a n s e s t e r i f i e d b y a l k a l i n e  w i t h diazomethane  and  s h o u l d be c o n v e r t e d  75I(+) s i n c e i t comprises  s t a t e photoproduct  (Figure  dibenzosemibullvalene  r o t a t i o n so obtained  iPr/iPr-57  o f thee n t i r e photoproduct  m a t e r i a l . The p r o d u c t s  and treatment  the  ester.  (S)-(+)-42  i t s absolute c o n f i g u r a t i o n should c l e a r l y  subsequent d e r i v a t i z a t i o n starting  sec-butyl  from d i e s t e r  Forp r a c t i c a l  configuration  that o f t h e major photoproduct reaction  because  c o u l d have a s i g n i f i c a n t and  from t h e c h i r a l  i n t o t h e same compound w i t h o u t m o d i f y i n g during  valid  t o o b t a i n i t s absolute c o n f i g u r a t i o n from t h e s i g n o f  rotation,  optically  n o t be  81)  (+)-52.  to The  give  the  unreacted hydrolyoptically  sign o f the optical  { [ a ] r ; = 1 4 . 5 , ( c = 0.12, CHCI3)} was o p p o s i t e t o t h a t  -203-  from  the  diisopropyl  indicates solid  dibenzosemibullvalene  t h a t the a b s o l u t e s t e r e o c h e m i s t r y  (S)-(+)-42  of  (compound 7 5 I ( + ) ) p o s s e s s e s  the  the  major  {(R)-4b,  (R)-8d) a b s o l u t e  stereochemistry,  pathway  the absolute stereochemistry of d i e s t e r  Figure  12-1  and  and  all-(S)-(-)-57.  establishes  This product  (R)-8b,  the  result from (R)-8c,  preference  for  ( + ) - 7 5 I shown i n  82.  Since arising  the d i b e n z o s e m i b u l l v a l e n e from  hydrolysis (+)-52  pathways  treatment  and  10%  (i.e.  reagent  NMR  Dimethyl  the  same,  73).  i t s h o u l d be  should  from  (751  This  was  give +  a  741)  of noted  that  our  of  90%  mixture and  confirmed  products  by  (7511  +  chiral  7411) shift  s t u d i e s on t h e o b t a i n e d s a m p l e o f 52 w i t h 1 e q u i v a l e n t o f  dibenzosemibullvalene  81.  arising  Figure  performed  Figure  are  esterification  (-)-52  respectively  Eu(hfc)3  and  "I"  absolute stereochemistry  as  in  the  case  of  compounds d e s c r i b e d  Conversion  the  (+)-52.  and  diisopropyl  earlier.  of the Photoproducts  Dibenzosemibullvalene  diethyl  from  (S)-(+)-42  into  the  -204-  (S)-(+)-42 PATH 1 2 - H  COOiPr  COOiPr  C00sBu(+)  sBu(+)00C  75I(+)  Figure  75II(+)  82. F o r m a t i o n  o f Dibenzosemibullvalenes  751  a n d 7511  from  (S)-(+)-42.  A  final  point concerning  t h e f o r m a t i o n o f (+)-75II i n t h e s o l i d s t a t e  involves the s o l i d state conformation starting  material  dibenzobarrelene the right  absolute o rl e f t  structure well  (S)-(+)-42.  The  t h e ene-dioate absolute  system  configuration  2i-screw  axes).  procedure  o f t h e enantiomorphous c r y s t a l  group  the  of  the  With  should  a  chiral  handle  normally be t r i v i a l  phase ( i . e .  i n t h e molecular and r e q u i r e only a  r e s o l v e d X-ray structure. Unfortunately, the d i s o r d e r present  sec-butyl  of  s t r u c t u r e a s 11M.12P o r 11P.12M r e q u i r e s t h e k n o w l e d g e o f  configuration  this  of  prevents  us from an experimental  i n  the  determination of this  -205-  iriformation  since  unambiguously isomorphic  the  established.  chiral  conformation  sec-butyl conformation However,  on  our  results  with  the  d i i s o p r o p y l d i e s t e r 2 3 , we c a n p r o p o s e t h a t t h e 11M.12P  shown i n F i g u r e  i n the c h i r a l  based  and s t r u c t u r e c o u l d n o t be  82 s h o u l d b e t h e r e a c t i n g m o l e c u l a r  structure  c r y s t a l s o f (S)-(+)-42.  P h o t o c h e m i s t r y o f t h e R a c e m a t e o f Compound 4 2 .  The  photochemical  differed (Table  results  significantly XX).  A  from  crystals  from the r e s u l t s o f  o f t h e r a c e m i c d i e s t e r 42  the  optically  pure  compound  r e d i s t r i b u t i o n o f t h e p h o t o p r o d u c t s was d e t e c t e d  and the  regioselectivity,  still  to  isopropyl  group,  ester  (31+31):(7+31).  Three  should  diminished out  p r o d u c t s were d e t e c t e d It  f a v o r i n g bonding at the v i n y l  of  the  i n relative  be d e s c r i b e d  Compounds  labeled  regioisomers, absolute  ratio  (75I+77II):(74I+74II) =  diastereomerically  different  b e n o t i c e d t h a t t h e two e n a n t i o m e r s o f t h e c r y s t a l s o f t h e  Each p r o d u c t has three  should  four  a  in 74  eight  possible  stereochemically  order  to  differ  establish from  stereochemistry  photoproducts  their  from  relative 75  compounds  in  labeled  structures.  that  compounds  of the dibenzosemibullvalene finally  (Figure  independent elements and a l l  compounds  compounds l a b e l e d " I " d i f f e r  e i t h e r a l l R o r a l l S, a n d  asymmetric (+)  they  " I I " in  are the  carbons,  differ  compounds l a b e l e d (-) d e p e n d i n g o n t h e i r r e s p e c t i v e e n a n t i o m e r i c handle.  the  l a r g e amounts ( 3 1 % e a c h ) .  s t a r t i n g m a t e r i a l s c a n g i v e up t o 83).  to  carbon next  from  sec-butyl  -206-  COO(+)sBu COOiPr  COO(-)sBu (all  I  COOiPr  S)  COOiPr. C00(+)sBu  COOiPr COOsBu(-)  COO(+)sBu  II  (all  Figure  R),  COO(-)sBu  83. S t r u c t u r a l P o s s i b i l i t i e s  (+)-sec-butyl/isopropyl-42.  COOiPr (-)sBuOOC  f o r the Photoproducts  From D i e s t e r  -207-  The f i r s t crystal  q u e s t i o n we a d d r e s s h e r e  lattice  skeleton,  that  on  the  r e l a t e s to the e f f e c t of the c h i r a l  stereochemistry  i s , the  relative ratio  of  the  dibenzosemibullvalene  of products  " I " versus  products  "II."  A s y m m e t r i c S y n t h e s i s by S o l i d S t a t e R e a c t i o n o f t h e Racemate o f 42.  If of  the r e a c t i o n of the racemic  the c r y s t a l l a t t i c e  s y m m e t r y , i t may  even though both enantiomers of  optically  imposition with was  d i e s t e r 42 o c c u r s  active  are present  products  o f any e x t e r n a l  from  chiral  1  synthesis, The crystals  the f e a s i b i l i t y  of  c a r r i e d out f o r the f i r s t  procedure  used  to  racemic  2  study  optically  of  racemic  42 s e l e c t e d  variations diesters  or  for  this  type  of  21  and  23, cannot'be  induction,  i n a unimolecular  the  asymmetric  a t random f r o m  to  mixtures  may  compounds, e i g h t p r o d u c t s  rotation  i n chiral  large  single  rotations,  either  Slightly the  the  case  of  optically  83) a n d two s t a r t i n g m a t e r i a l s .  larger  symmetric  of inconsistency  r e s u l t f r o m up t o t e n p o s s i b l e (Figure  asymmetric  c r y s t a l batches.  studied.  in  study  reaction.  six  specific  samples  without  phenomenon  induction  several  t a k e n as e v i d e n c e  as t h e o p t i c a l  generation  absolute  time  a l l the  products  step i n the present  i n t h e s p e c i f i c r o t a t i o n v a l u e s as compared w i t h  enantiomeric photolysis  negative,  active  i s a m o s t uncommon  The f i r s t  The r e s u l t s shown i n T a b l e X X I i n d i c a t e h i g h positive  control  starting materials,  o f t h e d i i s o p r o p y l d i e s t e r 23 was a p p l i e d  crystals  the  i n e q u a l a m o u n t s . The  influence,  o n l y one l i t e r a t u r e p r e c e d e n t . - ' to determine  generate  through  i n the these active  -208-  Table  XXI.  Solid  State  Induced  Optical  A c t i v i t y by P h o t o l y s i s o f  C r y s t a l s o f t h e Racemate o f D i e s t e r 42.  Sample  Weight (g)  %  Conversion  Q  (degrees)  [a] (degrees) D  1  0.0258  11.8  0.065  21.4  2  0.0217  14.9  0.071  21.9  3  0.0138  18.9  0.046  18.0  4  0.1029  12.1  -0.218  -17.2  5  0.1385  11.4  -0.303  -19.2  6  0.1005  11.5  -0.193  -16.7  Since  the disymmetric  with the c h i r a l on  crystals  influence of the  crystal  the c o n f i g u r a t i o n of the  their  final  in  o f compounds i P r / i P r - 2 3 a n d ( S ) - ( + ) - 4 2 , dibenzosemibullvalene  a l l - ( S ) ] we may s t a r t b y d i s r e g a r d i n g t h e n a t u r e and  lattice,  disposition  in  the  final  skeleton  based  photoproducts.  on  s h o u l d be  [all-(R)  or  o f the ester substituents  should t h e r e f o r e include conversion o f the t o t a l photoproduct a s i n g l e compound, c o n v e n i e n t l y a n d  analogy  our  resolved m a t e r i a l , the dimethyl dibenzosemibullvalene  Our  strategy  mixture  experience  with  d e r i v a t i v e 52.  into the  -209-  Extent of Asymmetric I n d u c t i o n i n C r y s t a l s of the  In  order  extremely  careful experimental  crystal  (0.1676  crushing, smaller  to have a c o n s i s t e n t account  and  o f 42 was  s e p a r a t e d i n t o two  portion  of the e n t i r e remaining  g)  was  (after  C H N ) . The  pure photoproducts,  2  hydrolyzed, by and  '-H NMR that  identical  r e s u l t as  ([Q]  d  =  by  ratio  o f 90:10  by k e e p i n g  measuring  m a t e r i a l b e f o r e and  e.e.  -14.4°,  by  The  =  •=  ( R ) - ( - ) - 4 2 (11.1 v e r s u s the  after  enantiomeric  the photochemical  The  8%).  The  t o 15  %  chromatographic  starting material with CHCI3)),  (c=0.15,  spectrum  and  of  pure  were  analyzed  this  sample  indicate  starting  an  material  80%.  t r a c k o f t h e s t a r t i n g m a t e r i a l mass (S)-(+)-42  by  composition  shown i n F i g u r e 84,  o r a e.e.  single  g.  w i t h the n i t r o g e n l a s e r  of the o p t i c a l l y  c o u l d n o t i c e t h a t t h e amount o f  reached  CHCI3),  an  divided  0.0434  w i t h d i a z o m e t h a n e t o g i v e d i e s t e r 52  i n the case  much a s t h e amount o f  and  large  the e x a c t e n a n t i o m e r i c  o f a n a u t h e n t i c r a c e m a t e o f 52,  Interestingly,  0.1232  e q u i v a l e n t s of Eu(hfc>3.  w i t h an e n a n t i o m e r i c  we  portions of  d e r i v a t i z a t i o n of the remaining  esterified  w i t h 0.2  the racemate, f i n e l y  ( 0 . 0 1 5 4 g) w e r e s e p a r a t e d  procedures 2  grown from  p h o t o l y z e d a t 0°C  the products  A  devised.  D  was  state reaction  was  ( [ a ] = -0.9°, ( c = 0 . 0 4 3 ,  compound  c o n v e r s i o n and  of the s o l i d  procedure  used to determine  sample  Racemate.  reacted  was  7.4  This conclusion  mg).  compositions reaction.  of  1.5  balance  the  times  as was  starting  -210-  |  l  l  l  l  |  i  u  i  70  Figure  |  6  84.  X  H  |  l  0  S 0  NMR  Spectra  |  40  of  |  I I  3 0  Racemic  I  I !  I  1 I I  2  |  M  0  1  10  0 0  ( t o p ) and O p t i c a l l y  ( b o t t o m ) D i b e n z o s e m i b u l l v a l e n e 52 A f t e r A d d i t i o n o f 0.2  eq. o f  PPu  Active  Eu(hfc) . 3  -211-  An  i n t r i g u i n g question that evolved  t h e c r y s t a l p h a s e t h a t makes t h e the  crystal  lattice  (-)-enantiomer.  It  f r o m t h e a b o v e r e s u l t was  ( + ) - e n a n t i o m e r 1.5  preferred  by  the  seems t h e l a t t e r  pure  t i m e s more r e a c t i v e i s  (+)-  alternative  or  to  crystal  that  phase.  obtained  It  seems  component i s the s o l i d  On  the R e a c t i o n  The  selectivity different  of  solid  more  the  topochemical  the  can  solid  reaction  solid  state  with  reactive  [(+)-42]  phase.  same  one  The  formation of  dibenzosemibullvalene  regio-  and  =  1 1  three  absolute  shall  see,  s t r u c t u r e s o f d i e s t e r 42.  diastereoselectivity  85:5:5:5),  not  of we  c o n t r o l l e d r e a c t i o n of  in  because  c o n t r o l , but because of a l o s s of s t e r i c process.  face  o f the most i n t e r e s t i n g c o n c e p t s  n a m e l y t h e r e a c t i o n c a v i t y . As we  state molecular  skeleton  m a n i f e s t a t i o n of the  rearrangement.  the  illustrate  (751:7511:741:7411  crystallization  was  (+)-enantiomer  In  the  control  of  other  racemate  (751:7511:741:7411 = 31:31:8:31) i s l e s s w i t h r e s p e c t t o t h a t i n the enantiomer  since  here  g e n e r a t i o n of the d i b e n z o s e m i b u l l v a l e n e  t h e r e s u l t s as a r i s i n g f r o m a " c a v i t y "  three d i f f e r e n t words,  o f the pure  the  o f the racemate i s a remarkable  state reactivity,  interpret  that  pure  Diastereoselectivity.  diastereomers  stereochemistry  therefore  the  obtained  s o l u t e i n pro-(-)-enantiomorphous  enantiospecific  i n the c r y s t a l s  from the products  of  i s t h e c o r r e c t one  the a b s o l u t e c o n f i g u r a t i o n o f the d e r i v a t i z e d products opposite  whether  pure  a loss during  of the  For  illustration  diisopropyl of  purposes  d i e s t e r 23 w h i c h  we  can consider a c r y s t a l  i sconverted into a c r y s t a l  42 b y i s o m o r p h i c r e p l a c e m e n t  by  iPr/iPr-23  c a n be  filled  with  a  s t r u c t u r e s o f 42 t h a t d e f i n e DC(+)  site,  or reaction  filled  d i f f e r e n t m a n n e r s . I n F i g u r e 85 we initially  crystal  enantiomorphous defined  racemate  represent  molecule  cavity,  initially  up w i t h m o l e c u l e s o f 42 i n f o u r such  lattice  space,  (D),  o f d i e s t e r 23 s u r r o u n d e d b y t h e f o u r  the different  by  lattice  phases  occupancy  occupancies,  i n the D  DU(+),  DU(-),  there  or  L  lattices  the enantiomer  [ ( + ) o r ( - ) - s e c - b u t y l ] o f 42 f i l l i n g  a r e two n o n - e q u i v a l e n t e s t e r s i t e s  C or  U.  i n the c h i r a l  As  we  P2^2^2^  two e s t e r s c a n b e d i f f e r e n t i a t e d a s "C" a n d "U" d e p e n d i n g carbonyl group.is close  with thev i n y l  (the  that give Dextro- or Levorotatory photoproducts) i s  and b y t h e l o c a t i o n o f t h e s e c - b u t y l group,  the  the  and DC(-). Every  The  of  of the  o f m o l e c u l e s o f 23 b y m o l e c u l e s o f 4 2 . I t  should be n o t i c e d t h a t every l a t t i c e occupied  lattice  t h e space  have  structure. on  t o C o n j u g a t i o n (-160°) o r U n c o n j u g a t e d  C ( l l ) - C ( 1 2 ) double  bond.  seen,  whether (-65°)  -213-  DO'-n Figure Diester  85.  The  DC(-)  F o u r Modes o f I s o m o r p h i c R e p l a c e m e n t  a  single  the pure enantiomers  occupancy,  DU(+),  where  without apparent c r y s t a l l o g r a p h i c disorder, corresponding by  to the C ester  group  (Figure  l a t t i c e - c o n t r o l l e d bonding at the v i n y l  group up w i t h lective  23  by  42.  C r y s t a l s b u i l t up w i t h present  of Diester  (path  12-1,  Figure  8 2 ) , and s i n c e  [(S)-(+)] the  is 85).  isopropyl  situated  iPr/sBu-42 substituent,  in  a  position  Here the r e a c t i o n  carbon next  to  the  the r e a c t i o n c a v i t i e s  a s i n g l e component, the r e a c t i o n i s h i g h l y r e g i o (85%).  of  and  occurs  isopropyl are  filled  diastereose-  -214-  In the  case o f the  w i t h e i t h e r (+)i n the at  C 86.  site, Reaction  diastereomeric the  the  r e s o l v e d compound, w i t h t h e  there  products  occupancy  w o u l d be  at the  t h i r d diastereomer,  partial  r e a c t i o n c a v i t y can  two  o n l y two  lographic  lattice  7 5 I ( + ) and  s i t e s would give r i s e  75I(-)  (Figure 86).  e i t h e r 7 4 I ( + ) o r 7 4 I ( - ) , c a n be  of  the c o r r e s p o n d i n g  (+)  can  r a c e m a t e , i t s h o u l d be alternative state.  or DC(+)  a r e a c t i o n c a v i t y c o n t r o l l e d process  disorder  model  filled  explain  noted that  (-)  The  those always  and  DU(-)  to  the  interpreted  o r DC(-)  in two  (Figure  a c c o m p a n i e d by  observed i n the  we  cannot  strictly  of  as  e n a n t i o m e r o f 42  results  t h a n 12-1  up  formation  the  where pathways o t h e r  to  i s o p r o p y l groups  o c c u p a n c i e s DU(+)  s e c - b u t y l group i n the C e s t e r p o s i t i o n , Although  be  (-)-42. I f the e s t e r o c c u p a n c i e s were s i m i l a r  c r y s t a l s o f the  the  Figure  or  racemate, every  a  with  87).  crystal-  case of  the  differentiate  an  take place  i n the  solid  -215-  (R)-(-)-sBu  (S)-(+)-sBu  DU( + ) PATH  12-1  COOiPr  COOiPr  C00(-)sBu  COO(+)sBu  75I(+)  Figure  86. L o s s  75K-)  of Diastereomeric Control  t r y b y Means o f O c c u p a n c y Enantiomers.  0^0 i n the Product  o f t h e Same C h i r a l L a t t i c e  Stereochemis-  S i t e b y two D i f f e r e n t  -216-  (S)-(+)-Sbu  (R)-(-)-Sbu  COO(+)sBu  C00(-)sBu  COOiPr  COOiPr  74I(-)  7AI(+)  Figure Disorder  87. L o s s  of  i n the C r y s t a l  Regioisomeric Lattice  of  Control  (R,S)-42.  by  Means  of  Positional  The S o l i d  State  While  some  briefly  of  discussed  respect and  P r o p e r t i e s and P h o t o c h e m i s t r y o f D i e s t e r  to  the  solid  i n Part  s t a t e c h a r a c t e r i s t i c s o f compound  I I I , some a d d i t i o n a l comments  t h e two s a m p l e s e m p l o y e d .  studies.  The  melting  v a r i e d by f o u r degrees  (Table  that  racemic  that could  of  solid  the  enantiomers the  (Figure  the p o s s i b i l i t y  with  than  that  of  crystal  point  crystals of both  o f the of  the  materials  of having  o f f i n d i n g any racemic and identical.  of a non-ideal  state  87A) v e r y  FTIR  spectra  of  the  This  solid  two  and Me/iPr-30.  I t was  see t h i s  hypothesis  explain  observed  from  diastereoselectivity  a c t i v e c r y s t a l l i n e m a t e r i a l s o f compound  the 31.  evidence  informasolution type I I .  samples  suggested i n the previous  form isomorphous c r y s t a l s w i t h  for  enantiomor-  c l o s e l y resembled the spectra obtained  g r o u p o f d i e s t e r 3 0 , a n d a s we w i l l  optically  single  a maximum m e l t i n g p o i n t , o r R o o z e b o o m  solid  t h e s e compounds may  the  i n d i c a t i o n was  that the melting  t h e two s p e c t r a w e r e e s s e n t i a l l y  d i e s t e r s Me/nPr-29 that  was  s t r o n g l y suggests the p o s s i b i l i t y  Interestingly, Me/sBu-31  (91-2°C)  of solutions of  state modifications. Instead  substantiate  crystals,  t i o n very  activity  the  i n KBr i n an attempt t o f i n d p o s s i b l e s p e c t r a l e v i d e n c e  different  phous  Indicating  (94-5°C). S o l i d s t a t e F T I R s p e c t r a o f c r y s t a l s  were o b t a i n e d two  45)  observation  lower  diffrac-  I , page  by the l a c k o f o p t i c a l  o p t i c a l l y p u r e f o r m was  pure  samples  confirmed  racemate  f o r X-ray  n o t undergone a spontaneous r e s o l u t i o n . T h i s  additional  with  o f t h e two  had  An  timely  points of single crystals  material  specimens.  seem  31 w e r e  C r y s t a l s grown w i t h o p t i c a l l y  r a c e m i c m a t e r i a l s were b o t h f o u n d t o be u n s u i t a b l e  tion  Me/sBu-31.  f o r the section  the racemic serves racemate  of  space  well  to  and the  Pure D i e s t e r  Me/iPr-31.  -219-  The and  glc  (R,S)-31,  (Table  XXII).  overwhelmingly the  determined i n contrast The  solid  state  to  selectivity  compound  42,  (S)-(+)-31  surprisingly  identical  was  state regioselectivity,  group.  This  i n the c r y s t a l s  preference  as  indicated  of  the  compares  diesters  XXII.  Relative Solid  well  Me/nPr-29  agreement w i t h o u r h y p o t h e s i s o f an isomorphous  Table  of c r y s t a l s of  i n Part I I I ,  f a v o r s the b e n z o - v i n y l b r i d g i n g step a t the carbon next  sec-butyl  observed  solid  w i t h the and  crystal  to  results  Me/iPr-30  in  structure.  State S t e r e o s e l e c t i v i t y  3  from C r y s t a l s  of  Compounds M e / s B u - 3 1 . Compound  Path A-I  / P a t h A - I I (%)  • P a t h B-I  / Path B-II  Me/(+)-sBu-31  42  55  ---  -3  Me/(+)-sBu-31  42  55  ---  -3  (%)  a) A b s o l u t e s t e r e o c h e m i s t r y o f t h e p r o d u c t s n o t known.  The two  insensitivity  diastereomers  o f the s o l i d  from  paths  s t a t e r e a c t i o n to the formation of  A-I  e n a n t i o m e r i c c o m p o s i t i o n o f t h e two and  requires further analysis.  t h e r a c e m i c compound a n d are  very  scarce.  reactivity  s h o u l d be  different  crystal  and  p a t h A - I I , and  crystalline  materials  Previous l i t e r a t u r e  the r e s o l v e d m o d i f i c a t i o n  These  studies  suggest  to the  that  is  different surprising  r e p o r t s on t h e s t u d y of  chiral  b e h a v i o r from the racemate  1  3  and  5  of  The the  apparently  a different solid  optically  identical pure  of  substrates  e x p e c t e d b e t w e e n t h e two p h a s e s a s a r e s u l t o f packings. - - *  the  state their  photochemical  materials  would  -220-  normally  suggest a spontaneous r e s o l u t i o n from t h e former. Such an event,  however, i s n o t o p e r a t i v e The in  simplest  Table  XXII  i n t h e c a s e o f t h e r a c e m a t e o f compound 31.  explanation would  o f t h e r e s u l t s shown i n t h e f i r s t  be that there  i sl i t t l e  preference  two columns  b e t w e e n t h e two  a l t e r n a t i v e pathways and t h a t b o t h c a n occur w i t h almost equal p r o b a b i l i t y i n t h e two s o l i d this  possibility,  results the  c a n be  solid  This  ( F i g u r e 88).  i ti s interesting obtained  A l t h o u g h we c a n n o t r u l e o u t  to notice  that  c o n t r o l on t h e r e a c t i o n  t h e same  face-selectivity.  c a n come a b o u t a s a r e s u l t o f t h e d i s o r d e r p r e s e n t  s o l u t i o n o f theenantiomers, which i ncontrast  42, c r y s t a l l i z e s  exactly  under c o n d i t i o n s where t h e r e a c t i o n p r o c e e d s i n  s t a t e with an absolute  possibility  solid  state materials  i n a racemic space  to that  i n the  o f compound  group. COOsBu  A-I,'  \  A-II  COOsBu  COOsBu MeOOC  COOMe  64A-I Figure  88.  Hypothetical  D i a s t e r e o m e r s 64A a s a  Result  64A-II Reaction of  a  F a c e - S e l e c t i v i t y o f t h e Rearrangement.  of Lack  Diester of  31  Lattice  to  G i v e t h e Two  Control  on t h e  -221 -  We  start  by  considering  extremes o f a s o l i d space  group.  that  (S)-(+)-31  a n d ( R , S ) - 3 1 a r e t h e two  s o l u t i o n o f the enantiomers that  Crystals of this  solid  the  racemic space group P I .  would imply sites, The  the existence  of  conformation  of the molecules f i l l i n g  the carbonyl-double  bond  0(4)-C(15)-C.(12)-C(ll) ene-dioate  89).  lattice  sites  In  the  would  (S)-(+)-sec-butyl  be  In Figure  pathway  A - I w o u l d be s i m i l a r  centers,  configurations all  89, a l a t t i c e  lattice  and  L.  the  and  a  i n the dibenzosemibullvalene  the  defined and  a d o p t e d by t h e  11P.12M  same  rendering  The  to  0(2)-C(13)-C(ll)-C(12)  respectively enantiomeric  enantiomer  of  "quasiracemic"  the  crystal D through  c o n t r o l l e d r e a c t i o n v i a pathway products  formed  at  64A-I(+) and 64A-I'(+) would p o s s e s s o p p o s i t e asymmetric carbons  the  two  absolute  (all S  or  c h i r a l h a n d l e and would  t o two g l c s i g n a l s a s o b s e r v e d f o r d i a s t e r e o m e r s .  In the case o f the s o l i d interesting  chiral  similar  c o n t r o l l e d r e a c t i o n at the s i t e  site  group  crystal  and w i t h c h i r a l i t i e s  R) b u t w o u l d p o s s e s t h e same ( S ) - ( + ) - s e c - b u t y l  give r i s e  an  spaces,  11M.12P  to a lattice  seem  crystallizes  enantiomeric  The two c o n f o r m a t i o n s  by  31,  racemic  i n a racemic space  and  these  angles  as  occupied  derivative  i n the c r y s t a l  which  c a s e o f t h e r e s o l v e d m a t e r i a l t h e two  lattice.  reaction  torsion  (Figure 89).  a  ( o r m i r r o r and g l i d e p l a n e s ) .  be d i s y m m e t r i c  s y s t e m w o u l d be d e f i n e d  (Figure  A-I'  equivalent  D a n d L, r e l a t e d b y i n v e r s i o n c e n t e r s  s t r u c t u r e of Me/iPr-30, should by  Crystallization  two  in  s o l u t i o n , as mentioned b e f o r e ,  t o be i s o m o r p h o u s w i t h c r y s t a l s o f d i e s t e r s M e / i P r - 3 0 in  pack  alternative  s o l u t i o n with the composition could  take p l a c e .  I f t h e r e were s u b s t a n t i a l  r e c o g n i t i o n between the disymmetry o f the c r y s t a l  L, a n d t h e m o l e c u l a r  chirality  o f t h e racemate  lattice  o f t h e two d i b e n z o b a r r e l e n e  sites,  D  enantiomers  (S)-(+)-31 and ( R ) - ( - ) - 3 1 , properly crystal  called lattice  64A-I(+), site  and  L and would  should  a  racemic  s i t e s D would molecules  compound.  be  ordered  Molecules o f (S)-(+)-31  r e a c t through pathway A-I  of  (R)-(-)-31 would  occupy  to  and  more  occupying  give  the c r y s t a l  product lattice  r e a c t through pathway A - I ' t o g i v e p r o d u c t 6 4 A - I ' ( - ) .  It  be n o t i c e d t h a t t h e p r o d u c t s g e n e r a t e d d u r i n g s u c h e v e n t s would  be  enantiomers  and would  Obviously,  our  observe  the s o l i d s o l u t i o n would  signals  give r i s e  experimental  to  a  results  single do  glc  not  signal  agree  (Figure  90).  with this since  we  c o r r e s p o n d i n g t o t h e two d i a s t e r e o m e r s .  F i g u r e 89. H y p o t h e t i c a l R e a c t i o n o f Enantiomeric Crystal  Lattice  Sites.  One  Enantiomer  of  31  at  Two  -223-  OsBu(+)  (-)sBuO 0  SITE D  ^  OMe  SITE L  PATH A - I  C00sBu(+) COOMe  64A-I'(-)  64A-I(+)  Figure eric  90.  Hypothetical Reaction  E n a n t i o m e r s a t Two  Enantiom-  Crystal Sites.  Suppose t h a t t h e r e ers  o f Two  of  lattice  diester sites  (S)-(+)-31  31  i s no c h i r a l and  the  two c h i r a l  w o u l d be o c c u p i e d  and  (R)-(-)-31.  r e c o g n i t i o n b e t w e e n t h e two lattice sites,  i n d i s c r i m i n a t e l y by  In Figure  91 i t c a n b e  the  as  we  saw  f o r compound 42.  This  D a n d L. The two  two  molecules  seen t h a t r e a c t i o n of  b o t h e n a n t i o m e r s o f 31 a t t h e same l a t t i c e s i t e w o u l d g i v e products,  enantiom-  diastereomeric  i s i l l u s t r a t e d by r e a c t i o n o f  -224-  (S)-(+)-31 64A-I(+)  and  (R)-(-)-31  through  pathway  A-I  to  give  diastereomers  and 64A-I(-).  OsBu(+)  OsBu(-)  SITE D PATH A - I  C00sBu(+)  COOsBu(-)  COOMe  COOMe  Cdb0  QCt-O  64A-I(-)  64A-I(+)  Figure Through  though  supported  only  o f Two E n a n t i o m e r s a t t h e E q u i v a l e n t R e a c t i o n  Equivalent Reaction  Even  racemic  91. Reaction  structural  by the l i k e l y  isomorphous  minor  Me/sBu-31.  Pathways.  X-ray  and  resolved  31. This  structural Substitution  Site  i s l a c k i n g , t h e above  relationship  i sreasonable  differences of  data  between  between  ideas are  Me/iPr-30  and  considering that there are diesters  Me/iPr-30  and  t h e i s o p r o p y l f o r t h e s e c - b u t y l compounds i n  -225-  the  PI  crystal  lattice  m o l e c u l a r volumes The  and shapes  m o l e c u l a r volumes  calculated  in  Kitaigorodsky  1 3  of  an .30  30 seems r e a s o n a b l e i n l i g h t o f t h e s i m i l a r  o f t h e two d i e s t e r s .  o f compounds  approximate j Bondi 1  a n c  3 1  Me/iPr-30  manner b y t h e g r o u p mentioned  v a l u e s r e c e n t l y updated by G a v e z z o t t i ^  Compound  The  and  4 4  much  Using  the  increment  C a l c u l a t e d Volume(A3) 327.3  31  344.1  coefficient  o f geometric s i m i l a r i t y ,  value  be  we a r r i v e a t t h e f o l l o w i n g :  30  better  can  increment approach o f  earlier.  e, i n t h e c a s e o f compounds  30 a n d 3 1 , c a l c u l a t e d w i t h t h e a b o v e v o l u m e v a l u e s , a  Me/sBu-31  than  the lower l i m i t  t u r n s o u t t o be  0.95,  o f 0.85 p r o p o s e d b y K i t a i g o -  rodsky. I t c o u l d have been e x p e c t e d t h a t occurred  the  have  molecular structures o f the sec-butyl enantiomers,  (R)  and  t o form an o r d e r e d racemate  would r e q u i r e s u b s t a n t i a l volume (S)-31  on  sites,  may  L, a n d t h e c h i r a l  (R)-and  crystal  recognition and  recognition,  chiral  chiral D  Chiral  between  some  differences  of  structural  between  the  both  D  and L i n t h e isomorphous  (R)-and (S)-31 would occupy  t o 30,  molecules  between  the  t h e two e n a n t i o m e r s  be n o t o n l y s t r u c t u r a l l y s i m i l a r t o e a c h o t h e r , b u t a l s o spaces  31.  of  spaces on t h e o t h e r .  similarity  e n a n t i o m e r s o f 31 w e r e a l s o v e r y c l o s e t o u n i t y ,  of  o f 31 i s o m o r p h o u s  one h a n d a n d t h e D a n d L l a t t i c e  However, i f t h e c o e f f i c i e n t  (S)  to  c r y s t a l s t r u c t u r e . That  two e n a n t i o m e r i c c r y s t a l  the  two would  lattice  i s t o say that sites  with  no  (or  little)  discrimination.  Although  i t  has  been  shown  t h a t the c o n f o r m a t i o n a l freedom  s e c - b u t y l s u b s t i t u e n t can f a c i l i t a t e polymorphism interesting  two  e n a n t i o m e r s o f 3 1 . The of  forming  c o e f f i c i e n t would a  disordered  g i v e u s some i n s i g h t  solid  s o l u t i o n of the  a c c o r d i n g t o t h e c r i t e r i a g i v e n by K i t a i g o r o d s k y We ers  occur  with  n o n - o v e r l a p p i n g volumes  the  (e >  groups  the  exception  b e t w e e n t h e two  represented  by  of  the  two  the  coefficient  volume e - 0.86  Kitaigorodsky, space o f the  of  still  a  methyl  group  between ( R ) - and allow  (S)-compound.  for  (44.6A ). 3  (S)-31 which  occupancy  enantiom-  s e c - b u t y l groups.  92.  from  The  the  two  I t i s apparent  that  n o n - o v e r l a p p i n g v o l u m e b e t w e e n t h e two e n a n t i o m e r s s h o u l d be  twice  the  0.85)  enantiomers r e s u l t  the dots i n Figure  into  enantiomers  c a n assume t h a t a c o m p l e t e m o l e c u l a r o v e r l a p b e t w e e n t h e  will  methyl  solubility, i t  t o c a l c u l a t e an a p p r o x i m a t e v a l u e f o r e i n the case o f the  is  probability  and s o l i d  of the  This should,  close  results  in  according  to a to  o f the (R)-enantiomer i n the  -227-  Figure  92.  Coefficient  It  Comparison  o f ( R ) - and (S)-31 i n Order  and o u r p h o t o c h e m i c a l r e s u l t s  t h e r e a c t i o n m o d e l s we h a v e p r o p o s e d . of  Determine  Furthermore,  the  enantiomers recognition.  justify  crystallographic  s e c - b u t y l c o n t a i n i n g compounds h a s b e e n d o c u m e n t e d a n d  f o u n d t o p r e s e n t d i s o r d e r as a r e s u l t o f a n o n - s t a t i s t i c a l isomorphism.  their  of Geometrical Similarity ( c ) .  seems t h a t t h e a b o v e c r i t e r i a  behavior  to  In  this  manner,  indiscriminately f i l l  as  we  have  proposed,  often  conformational  t h e two  each o t h e r ' s spaces w i t h o u t  sec-butyl  any  chiral  -228-  Our m o d e l s h o u l d t h e r e f o r e c o n f o r m t o t h e one o b s e r v e d spaces  are  for diester  to a c r y s t a l  30, w h e r e  the  f i l l e d w i t h o n l y one e n a n t i o m e r  modification,  a n d w i t h two e n a n t i o m e r s  occupancies are s t a t i s t i c a l ,  we  a c c o r d i n g t o t h e d a t a shown i n  Table XXIII. of Diesters  Proposed  of  Table  (S)-(+)-31 (R,S)-31  It  lattice  o f 31 i n t h e o p t i c a l l y  31  in  the  racemate.  i n the Isomorphic  Lattice  groups)  ._ L  ._  50%  50% ( S ) - ( + )  50%  2 5 % ( S ) , 2 5 % (R)  25% ( S ) , 25%(R)  t h a t the D and L s i t e s  t h e two d i f f e r e n t solid  state  are c h i r a l . lattice  the  structures  Site  (S)-(+)  a r e e n a n t i o m e r i c and  the conformations o f the d i b e n z o b a r r e l e n e - d i o a t e s t r u c t u r e s the a l k y l  If  Crystal Structures  50%  s h o u l d be r e c a l l e d  active  and r a c e m i c ) .  I) 30  enantiomeric  XXIII:  Occupancies  Crystal  ^  similar  can represent the three c r y s t a l  30 a n d 31 ( o p t i c a l l y p u r e  j  two  structure very  that  (even  ignoring  M o l e c u l e s o f one o f t h e e n a n t i o m e r s  o f 31 i n  sites will  t h e r e f o r e be  s i n c e t h e y c o n t a i n two d i s y m m e t r i c  diastereomeric  elements.  in  the  The  Solid  The in  State  solid  P r o p e r t i e s and  Photochemistry of Diester  s t a t e p h o t o c h e m i s t r y of d i e s t e r Et/sBu-39  i t s r e s o l v e d m o d i f i c a t i o n . The  be  slightly  substituent A-II  (refer  in  favor  ( 6 9 % ) . The to  of  regioselectivity  bonding  at the v i n y l  Figure  73)  was  similar  of  disordered No of  which  t o deduce  explored  solid  solution  of  more s t r u c t u r a l  information,  only  turned out  to  carbon next to the e t h y l  i n the  A-I  the enantiomers  and  optically  result i s indicative  f u r t h e r a t t e m p t s w e r e made t o a n a l y z e t h i s  lack  again  i n a racemic  compound due  a n d o f an i s o m o r p h o u s  space  to  the  compound  from  information.  T a b l e XXIV. R e l a t i v e S o l i d Compound  observed  to that observed  s a m p l e s o f M e / s B u - 3 1 . I t seems t h a t t h i s  group.  was  d i a s t e r e o s e l e c t i v i t y between the pathways  active a  Et/sBu-39.  State  S t e r e o s e l e c t i v i t y from  Crystals  of  Et/sBu-39  Compound  Path 1 /  Et/(+)-sBu-39  ---  69  Path 2  (%)  ---  Path 3 / 14  Path 4  (%)  .  17  Concluding Remarks.  All  the p o s s i b l e a l t e r n a t i v e s a v a i l a b l e to o p t i c a l l y  are v e r y i n t e r e s t i n g from the p o i n t o f view o f s o l i d stereochemistry  o f the products i n the s o l i d  a c t i v e compounds  state reactivity.  s t a t e , a s we  have seen  The  i n the  -230-  case o f t h e di-w-methane rearrangement, the  local  cavity.  microenvironment  Even i f  the  one  of or  the two  b e t w e e n t h e r a c e m i c compound a n d by  Pedone  molecular  and  Benedetti - ^ 1  environment  can  be  s o l u t i o n of the  The  can  be  e i t h e r D o r L, cavities,  i n any  viewed  racemic L,  constitution  can  occur  chiral  reaction cavity,  in  when  center,  different orientations.  ers  and  the r e g i o s e l e c t i v i t y There  are  R  have  solid  different or  in  state reaction  symmetry.  Enantiomorphous  of the racemate  enantiomeric reaction  cavity,  enantiomeric effects  reaction  on t h e  configuration  of  product a  the c h i r a l i t y  c r y s t a l s of the pure  will  give products  newly of  (Figure 93).  The  (space group  The  solid  state  the and  enantiom-  according  to  site.  r e p o r t s d e a l i n g w i t h the unique in solid  has  chiral  f i l l e d by d i f f e r e n t e n a n t i o m e r s  solutions  optically  were found t o c r y s t a l l i z e  enantiomers.  a  While  both  induced a t each r e a c t i o n  resolved modification the  slightly  of  solid  state  enantiomers.  One  c o n c e r n e d w i t h s e c - b u t y l c o n t a i n i n g compounds s u c h a s  d i a c r y l a t e 76  compound 76  proposed  dimensional  alternatives  i s c o n t r o l l e d by  c a n be  few l i t e r a t u r e  also  crystal  absolute  o r S,  chemical p r o p e r t i e s encountered is  reaction  similarities  three  at least  amounts. D r a m a t i c the  D o r L, w h i c h  crystals  the  will  equal  in  racemic  the  modification the  of those  as h a v i n g o n l y one  crystals  and  generated  and  by  enantiomers.  D  of  operate,  e x p e c t e d t o be  influenced  structural  s t e r e o s p e c i f i c i t y of a l a t t i c e - c o n t r o l l e d  crystals  vinyl  molecule  to  b e e n shown t o d e p e n d d r a s t i c a l l y on  such,  reacting  the enantiomorphous  when c h i r a l m o l e c u l e s c r y s t a l l i z e solid  profoundly  dimensional  were  5  c a n be  a c t i v e and  i n the c h i r a l  racemic  space  P I ) as a r e s u l t o f s o l i d  group  the  forms of  the  solubility  of  i n t e r m o l e c u l a r arrangement between the  m o l e c u l e s o f t h e d i a c r y l a t e 76 was according  to  the molecular  packing  indicated i n the f i g u r e , the absolute  motif  two e n a n t i o m e r i c  phase.  The  disordered formed.  chiral  motifs  D  sec-butyl  L  groups  were  That the extent  a single chiral  y'  Compound  2n  dimerization  i n Figure of  the  93. As  cyclobutane  on  the  enantiomorphous  shown t o be d i s t r i b u t e d i n a diastereomeric  products  was  o f t h e a s y m m e t r i c i n d u c t i o n was q u a n t i t a t i v e was g r o u p s a n d r e p l a c i n g them b y m e t h y l  esters  photoproduct.  Y  FOUR DIFFERENT  DIASTEREOMERS  76  X = (+)- or Y -  +  arrangement which can occur i n  depending  manner so t h a t a m i x t u r e o f f o u r  shown b y r e m o v i n g t h e s e c - b u t y l to give  and  present  configuration  carbons i s determined by the i n t e r m o l e c u l a r the  f o r 2n  suitable  (-)-sBu  COOET  Z - CN Figure  93. A s y m m e t r i c S y n t h e s i s  i n C r y s t a l s o f V i n y l D i a c r y l a t e 76.  -232-  PART V.  LUMINESCENCE STUDIES ON THE  The light  phenomenon  whereby  a s u b s t a n c e changes  i s c a l l e d photochromism.  shown  that  DIMETHYL D I E S T E R  Studies  1 5 4  t h e change i n c o l o r  i s due  on  18.  c o l o r upon a b s o r p t i o n  photochromic  systems  from t h a t o f the o r i g i n a l  or  may  material.  Photochromism  be r e v e r s i b l e  depending on the p r o c e s s from w h i c h i t o r i g i n a t e s . ism  is  often  associated  with  light-induced  or  Reversible  tautomeric  unsaturated  systems  formed  chemical process  a s t h e e n d - p r o d u c t o r a s an  The  detection  of  a  absorption or reflectance is  irradiated  of  intermediate. 1  i t  example  absorbs  p r e c u r s o r compound sible). The  1  5  3 4  and  conjugated results  photoproduct  from  may  be  3 4  i s u s u a l l y c a r r i e d out The  photochromic  by  species  a t an a b s o r b i n g w a v e l e n g t h so i t c a n r e a c t and g e n e r a t e  of  d e t e c t i o n o f the r e a c t i v e i f  system 1  analyzed The  w i d e l y used f o r the study o f r e a c t i v e  only  colored  spectrophotometry. -  d i f f e r e n t wavelengths.  sophisticated  a  photochromic  colored species which i s i n turn light  I r r e v e r s i b l e photochromism where  photochrom-  phenomena  i s o m e r i z a t i o h s where the a b s o r p t i o n p r o p e r t i e s o f  an i r r e v e r s i b l e  species  irreversible  cis-to-trans  a r e changed.  have  to the f o r m a t i o n o f a photoproduct  w i t h an a b s o r p t i o n spectrum t h a t d i f f e r s starting  of  at  detecting  (indirect  absorbing  or  reflected  technique of f l a s h spectroscopy, - 1  i n t e r m e d i a t e s , c a n be  these  wavelengths  detection,  3  considered  t r a n s i e n t photochromism.  i n t e r m e d i a t e by different  with  the  techniques  The is  3  a  direct  possible  compared t o those o f the  however,  is  often  also  pos-  6  detection  o f a p h o t o c h r o m i c system by making  spectroscopy i s also possible  in  favorable  use o f luminescence  c i r c u m s t a n c e s . - ^ Here 1  3  the  colored  species  detection instead larly  is  generated  i s p e r f o r m e d by of  i t s absorption  to  the  high  s t u d y a r e m i n i m i z e d by and  detection.  onset  responsible  for  envelope can  s o m e t i m e s be  of  the  excitation  "colored"  the  use  of  systems, ciently A  the  species.  and  the  is  opaqueness of  the  the  The the  two  the  species  as  absorption  for  the  study  P2^2^2^ and was  Et/Et-21  Pbca dimorphs r e s p e c t i v e l y ) .  selected  as  a representative  reported  in this  section.  diester  18  the  is  This  was  most r e a d y a v a i l a b l e and  compound i P r / i P r - 2 3  was  of  the  (the only the  dimethyl  based  for  have a  suffi-  yield.  in this  iPr/iPr-23, The  possible  photochromic  t h e s i s were detected  latter  their  Me/Me-18  the  the  were  in  diester  on  found easily  exceptions  example t o p e r f o r m most o f  selection  compounds o b s e r v e d t o p r e s e n t t h e see,  and  emission  luminescence  of  solid  Me/Ph-37,  the  common l i m i t a t i o n  from t h e i r  s t a t e luminescence p r o p e r t i e s  levels  the  under study should  studied  valuable  properties  o r p h o s p h o r e s c e n c e quantum 11,12-diesters  under  energy  to  i n t e r e s t i n g p h o t o c h r o m i c b e h a v i o r t h a t c o u l d be  diesters  problems  species  shape o f  to present  the  is particu-  measuring the  i m p o r t a n t r e q u i r e m e n t and  that  l a r g e number o f t h e  By  its  front-surface excitation  the  and  1 5 4 , 1 5 9  also obtain  but  phosphorescence)  solids.  between  spectroscopy  fluorescence  before  luminescence band gives  difference  can  luminescence  large  of  species.  An  as  (or  used to e x t r a c t i n f o r m a t i o n  emitting  however,  crystalline  observed t r a n s i t i o n s ,  s p e c t r u m one  new  manner  p e r f o r m i n g measurements by  regarding  nature  of  concentration  information  the  same  spectrum. Luminescence spectroscopy study  The  1 5 8  the  measuring i t s fluorescence  w e l l s u i t e d f o r the  related  in  studies  fact  that  e a s y t o p u r i f y among a l l t h e  phenomenon d i s c u s s e d  a l s o used i n s p e c i a l  h e r e . As  circumstances.  we  shall  -234-  General  Observations.  When  i r r a d i a t e d with the nitrogen l a s e r ,  s a m p l e s o f compound 1 8 p r e s e n t e d ized  as  the  until  A f t e r about f i v e  temperature,  i t was  maintained  blue  to possess  a  corresponding  experiments  significant  new  until  (Figure 94c). contribution  di-rr-methane  specimens RE),  that,  The l a t t e r  from  the  compound  the  time  has  already  to  (RE)  by  that  a  slightly  fluorescence  60-63).  of  of  the  Additional  t h e RE d i s a p p e a r s  resolution  found  photoproduct  from  there  o c c u r r e d a b o u t 15% r e a c t i o n .  any d e l a y w i t h i n t h e time  was this,  e m i s s i o n was  faces u n t i l  at  decrease  Following  Me/Me-52, t h e  ( i r r a d i a t e d on a l l c r y s t a l  there  replaced  compound  infra)  was f o u n d  emission  r e a c t i o n ( s e e pages  by  (vide  ( F i g u r e 94b).  i t was  character-  dibenzobarrelene  intensity red  and powdered  later  irradiation  strong  dibenzosemibullvalene  our  single i s  no  The RE  instrument  j i s e c ) , a n d seems t o b e due t o a n a l l o w e d t r a n s i t i o n ( f l u o r e s c e n c e ) . s p e c t r u m was i n d e p e n d e n t o f t h e e x c i t a t i o n w a v e l e n g t h  could  be  single  o r powdered  reproduced  without  a  nitrogen  r a t e ) and r a p i d l y Perkin-Elmer  difficulty  from  powdered samples  of  (see below)  4 3  and  sample t o sample e i t h e r as  crystals.  For most e x p e r i m e n t s , with  a  luminescence  appeared without (40  fluorescence  intensity  indicated  crystalline  The  in  the concurrent  of  by  seconds o f  f o r a b o u t one a d d i t i o n a l m i n u t e  different  trace  the  replaced  t h e RE d e c r e a s e d  from  a strong blue emission  fluorescence of the corresponding  (Figure 94a). ambient  single crystals  laser  ( 3 3 7 . 1 nm, 330 mW  transferred  LS-5  to  the  spectrofluorimeter.  Me/Me-18  were  irradiated  a v e r a g e p o w e r , 20 Hz  low The  temperature  repetition  device  experimental  of  the  observations  presented  here  continuous  could  sources  also  such  be  as  repeated  a  400  ter  t h e weak p u l s e d did  not  x e n o n lamp o f the  produce  observable  behavior.  This  crystalline  dibenzobarrelene  but  indicated  requires a relative  red-emitting only  detect  qualitatively matrix detected.  species. the  that  the  Perkin-Elmer  room  d i e s t e r s i s not  dibenzobarrelene  fluorescence  a  strong  in  spectrofluorimeRE  photochromic  state.  At  phosphorescence  of  phenomenon  to accumulate  solution  which  nm  Irradiation  specific  i n order  mentioned that  solid  the  a laser  be  cyclohexane)  m e r c u r y lamp (337  LS-5  of  intense  temperature photochromism  large photon i n t e n s i t y  I t should  with  Lomb m o n o c h r o m a t o r ) .  intensities  from t h a t o b s e r v e d i n the  (methyl  irradiation  W high pressure  w a v e l e n g t h s e l e c t e d t h r o u g h a B a u s c h and with  by  the  we  could  does  not  differ  77K  in  glassy  could  also  be  -236-  350  400  450  500  550  600  650  700  750  800  (wavelength  F i g u r e 94. Irradiated  at  Uncorrected 337  nm:  Emission  of  (a) As i t Appears  Crystals  of  Diester  Me/Me-18  D u r i n g t h e F i r s t 5 Seconds,  D u r i n g t h e F o l l o w i n g 60 s e c ( s p e c t r u m t a k e n a t maximum i n t e n s i t y ) (c) of  After  t h e Luminescence  i n (b) had Disappeared  D i b e n z o s e m i b u l l v a l e n e 52 i s I n c l u d e d i n t h e Same  That  t h e RE o r i g i n a t e d f r o m a s p e c i e s n o t  crystalline  samples,  species  i n d u c t i o n time r e q u i r e d t o dependent t h e r m a l decay  "X",  detect  and from  could  i t , but  nm)  (The S o l u t i o n  (b)  , and, Spectrum  Figure).  present  initially  i n the  be d e t e r m i n e d n o t o n l y by t h e also  from  Its  i t s fluorescence excitation  temperature  spectrum.  -237-  ,  Observations  at Different  Red-emitting source, kept then  samples  i n the dark  analyzed  Temperatures.  that  had  been  removed  f o r a s l o n g a s -3 m i n  i n the spectrophotometer,  from  (ambient  were s t i l l  RE.  When t h e r e d - e m i t t i n g s a m p l e s w e r e k e p t  i n dark  and  then  that  vanished. seconds  re-irradiated, Interestingly,  i t  was  t h e RE  noticed  could  be  p h o t o l y s i s time w i t h the l a s e r .  i n terms o f a r e l a t i v e l y  irradiation  temperature),  found  the  longer  RE  had  by  T h i s r e s u l t has  and  to present  for  regenerated  l o n g l i f e t i m e and  the  the  periods  completely  another  been  eventual thermal  five  interpreted  decay  of  the  red-emitting species. Laser  irradiation  temperatures  (77,  of c r y s t a l l i n e  155,  200,  and  samples performed  230  K),  d i f f e r e n t p h o t o p h y s i c a l and p h o t o c h e m i c a l (1 h ) w i t h t h e n i t r o g e n l a s e r a t  77  K  original  of  the  fluorescence  emission  strong long l i v e d emission phosphorescence 6 3 ) . No  of  was  observed  at  155  K,  on  a f t e r about f i v e  when t h e i r r a d i a t i o n was  could  be  observed  from  the  red  emitting  and  species  X  at  change  in  the  relatively as  the  ( s e e F i g u r e 28b,  page  glc  other  assigned  analysis  hand,  b u t no  of  these  resulted  i n the be  c o n t i n u e d f o r a s l o n g a s two  hours.  The  us  seconds,  irradiation  could  the  Instrumental l i m i t a t i o n s prevented  the  substantially  compound. A  observed  by  no  different  reaction  r e d e m i s s i o n p e r s i s t e d f o r the e n t i r e decay  in  diester  detected  in  Prolonged  the dibenzobarrelene d e r i v a t i v e  Photolysis  a p p e a r a n c e o f t h e RE  behavior. resulted  readily  t r a c e o f r e a c t i o n c o u l d be  crystals.  resulted  at four  irradiation species  time  from  from measuring  temperatures  and  which  no  apparent  i t originates.  the thermal decay  o t h e r t h a n 77 a n d  293  of K.  -238-  Attempts,  h o w e v e r , w e r e made t o m e a s u r e t h e t h e r m a l d e c a y o f X  Samples  irradiated  t h e LS-5  s p e c t r o f l u o r i m e t e r (77 K) w e r e shown n o t t o p r e s e n t  able  decay  intensity  in  was  intensity  was  available  from  extremely us  and one  K and p u t  after  monitored  a t 660 nm  by e x c i t a t i o n  sampled  every  a 20 m i n p e r i o d .  lifetime  was  accurate  (70  luminescence  min)  t h e RE  by  observ-  luminescence The  emission program  I t was  the  emission  and  excitation  spectral  a t 200  and  230  at  200  K were c h a r a c t e r i z e d by  reactivity.  K resulted  contrast,  at  230  Photolysis  i n no in  apparent  the  the for  appearance more  (visual detection)  accumulation  of  2%  K the r e a c t i o n o c c u r r e d t o a time  (10 m i n ) .  e n h a n c e d c h e m i c a l r e a c t i v i t y and by  The  than  293  of  larger  K  irradiation  the b r i e f  duration of  phenomenon as d e s c r i b e d above.  Excitation  The  In  of  temperature.  (5%) i n s h o r t e r p h o t o l y s i s  dominated  The nm.  K.  o f t h e r e d - e m i t t i n g s p e c i e s a t 77 K t h a t a l l o w e d  change i n the r e d e m i s s i o n i n t e n s i t y b u t  conversion  any  30 s e c w i t h t h e a i d o f t h e " k i n e t "  i n c r e a s e of the photochemical  photoproduct.  a t 337  77  accessory  the PECLS-I s o f t w a r e p r o v i d e d by P e r k i n - E l m e r .  irradiations  hour  i n the low temperature  intensity  measurements a t t h i s The  155  t h e RE  long  to perform  at  at  Spectrum of the Red-Emitting Species.  luminescence  indicating  that  excitation  t h e RE  i s due  spectrum  i s the most  convincing  evidence  t o a p h o t o c h e m i c a l l y i n d u c e d phenomenon i n  the c r y s t a l l i n e dibenzobarrelene d i e s t e r s .  P r o v i d e d t h a t one  species  (X)  -239-  is  responsible  f o r a given emission, t h a t quenchers are absent,  quantum y i e l d i s i n d e p e n d e n t o f w a v e l e n g t h , light  source  and  detector  are  used,  and t h a t a p r o p e r l y the  excitation  to the a b s o r p t i o n spectrum o f the e m i t t i n g s p e c i e s .  that  emission  envelope  shown  e x c i t a t i o n wavelength suggests the  observed  luminescence.  q u e n c h e r s seems u n l i k e l y giving and  r i s e t o t h e RE.  the quencher  donnor.  by the i n s t r u m e n t resemble The f a c t from  F i g u r e 94b i s i n d e p e n d e n t o f t h e  In the present  have  a  the  case, low  lower  the p o s s i b i l i t y of having  energy  lying  for variations  that the e x c i t a t i o n of  the  The e x c i t a t i o n the  emission  (660  nm).  of  the  transition  excited  state  band  than  of  the  At  completely  composed  18 i n d i c a t e s t h a t t h e  nature.  i n F i g u r e 95 was  by  o b t a i n e d by  two  band  systems.  An  a t -325 nm a n d h a s a maximum  wavelengths  seen  the  setting  longer  than  410  nm,  intense intensity  where  p r e v i o u s b a n d becomes v e r y l o w , t h e r e i s a b a n d  t h a t t h i s band system extends  of the red emission begins. of  closely  different  c h a r a c t e r i z e d b y t h r e e r e l a t i v e l y weak maxima a t 4 3 0 , 455 a n d 525  end  the  a t t h e maximum o f t h e e m i s s i o n b a n d o f t h e RE  apparently starts nm.  is  spectrum o f d i e s t e r  spectrum presented  monochromator  c e n t e r e d a t 366  onset  process  i n t h e lamp i n t e n s i t y a n d s h o u l d  s p e c t r u m o f t h e RE  absorption  The s p e c t r u m i s  absorption  be  in  s p e c t r u m , shown i n F i g u r e 9 5 , i s a l s o c o r r e c t e d  r e d - e m i t t i n g s p e c i e s , X , has a d i f f e r e n t  can  fact  the s o l i d s t a t e a b s o r p t i o n spectrum of the r e d - e m i t t i n g s p e c i e s .  that  intensity  The  1 6 0  Q u e n c h i n g s h o u l d n o r m a l l y be a n e x o t h e r m i c  should  should  t h a t t h e r e i s o n l y one s p e c i e s i n v o l v e d  i n view of  The e x c i t a t i o n  1 6 1  in  calibrated  spectrum  correspond the  that the  excitation  system nm.  It  t o up t o 5 7 0 - 5 8 0 nm w h e r e t h e  I t s h o u l d be p o i n t e d o u t t h a t  spectrum probably  the  the  left  does n o t r e f l e c t t h e a b s o r p t i o n  -240-  spectrum o f the r e d - e m i t t i n g species. At wavelengths s h o r t e r than the  absorption  of  s h o u l d become v e r y  the crystal matrix  (the dibenzobarrelene  i n t e n s e , so t h a t i t p r o b a b l y  325  nm  compound 18)  can a c t as a f i l t e r  t o the  s h o r t e r w a v e l e n g t h a b s o r p t i o n b a n d s o f X.  300  350  400  450  500  550  600  ( w a v e l e n g t h nm)  Figure (X)  95.  Corrected  i n Crystalline  E x c i t a t i o n Spectrum o f t h e R e d - E m i t t i n g  S a m p l e s o f D i e s t e r 18.  Species  -241-  Observatlons  Our been the  at D i f f e r e n t Wavelengths.  analytical  a  i r r a d i a t i o n s w i t h the n i t r o g e n l a s e r  fortunate circumstance  i n view of the  compound t h a t o r i g i n a t e s t h e  assigned  yet),  and  from the  any  RE  366  nm,  no  photochemical r e a c t i v i t y  On  the  o t h e r hand, samples f i r s t  chemical  reactivity  The  313  crystal, incident  nm  species.  irradiation.  The  significant  f r o m e x c i t e d 18 seems  l a c k o f RE observation  quite  e x i s t i n g between the  absorption  of  the  barrier  i f the  be  a relatively  w h i c h may  s i n g l e t or t r i p l e t )  singlet  red-emitting species  o f e n e r g y t r a n s f e r , h o w e v e r , may may  18,  and  at  presented observed. 366  compound  of  nm the  in  to  absence of the  energy  red-emitting outstanding of  o r i g i n a t e from  18  possibility to other  and  lack a  s t a t e compound. The  with respect  the  dibenzobarrelene  i s i n t e r e s t i n g t h a t the s t a t e may  18.  produce  then at  phosphorescence  o r i g i n a t e from the  a l t e r n a t i v e s a v a i l a b l e to the e x c i t e d  observed  not  i n view of the  is a triplet  i n e f f i c i e n t process  not  monopolize a l l the  t h a t i n d i c a t e s the  It  have  I t was  c o u l d be  and  abundant  a remarkable f a c t  energy t r a n s f e r from p a r t of the  RE  nm  upon e x c i t a t i o n  RE-species.  from  phenomenon.  most  fluorescence  have  a d i r e c t c o r r e l a t i o n between  t h e RE the  we  red emitting species,  same t i m e no  diester  (either  itself.  i r r a d i a t e d a t 313  i s a b s o r b e d by  nm  r e a c t i v e . Samples i r r a d i a t e d  band s u g g e s t i n g  dibenzobarrelene  This  a t the  o f Me/Me-18 and  light  the  i s a very  transfer  the  and  (which  at ambient temperature d i d  n e a r t h e maximum a b s o r b a n c e o f t h e  d i s p l a y e d t h e RE  overlap  red-emitting species X  i n s p i t e of being photochemically  clearly  18  nm  337  substantial absorption  red-emitting species  t h a t s a m p l e s i r r a d i a t e d a t 313  at  that  of  spin lack i t  f a s t e r decay  -242-  What i s t h e P r e c u r s o r o f t h e R e d - E m i t t i n g  S e v e r a l m o d e l s c a n be (RE)  in crystalline  models can  be  red-emitting (18),  order  species  (IMP).  into  (X)  two  X,  singlet  equations  (the  1 and  diester  2 18.  two  in  that  and  IMP  differ 18  p a r t i c i p a t i o n of diester first  t h r e e , and  more t r i v i a l  18.  RE  The  involvement  of both,  on  18.  whether  the  molecules  not  an  proposed i n  thermal  barrier  form a t 77K).  p a t h w a y s g i v e n by  o f an  pathway  4  impurity,  In  requires  Before  equations  IMP. the  w h i l e pathway 3 would not  g i v e n by  These  o r i f i t comes f r o m  f o r the  does  The  equations  we  3 and  should 4.  3  the  and  latter  involvement necessitate  engaging i n a systematic study  most i n t e r e s t i n g p o s s i b i l i t i e s ,  alternatives  as  the r e d - e m i t t i n g s p e c i e s X o r i g i n a t e s  the  molecules  depending  f o u r a l t e r n a t i v e p a t h w a y s c a n be  4 a r e c h a r a c t e r i z e d by pathways  luminescence  such  seem t o i n d i c a t e ,  formation  or t r i p l e t  red  diesters  a l l of which should account  its  pathways g i v e n by  groups  the  o r i g i n a t e s from the d i b e n z o b a r r e l e n e  I n F i g u r e 96,  during  for  samples o f d i b e n z o b a r r e l e n e  subdivided  to generate  observed  from  proposed to account  as o u r p r e v i o u s e x p e r i m e n t s  impurity  Species?  of  eliminate  of the the the  -243-  hu'  1)  18  2)  18  > 16*  ----  ->  1  [X]  > Singlet  Product.  hu'  >  1  18*  >  3  18*  >  [X]  >  52  hu'  3) IMP  >  [X]  -  >  Product  hi/' 4)  18 + IMP  >  [18-IMP] - ( X )  >  Product  hu"  5) X  >  6) X*  > X + hi/'''  F i g u r e 96. and  was  P o s s i b l e Formation  Produced  by an  involvement  a n a l y z e d by  tive  (Red  Luminescence)  Pathways f o r the R e d - e m i t t i n g  B i p h o t o n i c Mechanism f o r the Appearance o f the  I s t h e RE  The  X*  two  purification  of  under  conditions  first  compound Me/Me-18.  where  1 8 ) . The  that  i m p u r i t y was and  readily  contained  p u r e when  A  detector  exhaus-  analyzed  on by  (l/2000th) as  e v i d e n t from UV-absorption  and  crystal  was  batch,  a trace, blue luminescent  luminescence  RE  response  i d e n t i f i e d as a n t h r a c e n e  e x c i t a t i o n s p e c t r a . The  100%  similar  p u r i t y o f 18 a l s o seemed t o be  actually  involved  Most s t u d i e s were p e r f o r m e d  (assuming  f l u o r e s c e n c e measurements i n s o l u t i o n . found  method  i m p u r i t i e s o f t h e o r d e r o f 0.05%  c o u l d have been d e t e c t e d e a s i l y for  Red-Emission.  a t r a c e i m p u r i t y as b e i n g r e s p o n s i b l e f o r t h e  s a m p l e s o f Me/Me-18 t h a t h a d b e e n shown t o be glc  X  Impurity?  p r i n c i p a l m e t h o d s . The of  Species  by  however,  impurity. This  i t s fluorescence emission  spectrum  of anthracene,  however,  -244-  c o u l d o n l y be d e t e c t e d excited  state  by  direct  i n the wavelength  excitation  into  r a n g e b e t w e e n 345  its  a n d 410  S a m p l e s c o n t a i n i n g a n t h r a c e n e p r e s e n t e d no d i f f e r e n c e cence  nm  in  samples,  chromatographic  were  passes  exhaustively  (Figure  their  through  silica'  re-purified  gel  using  s o l v e n t a n d b y a number o f r e c r y s t a l l i z a t i o n s . samples  were  anthracene  irradiated,  they  presented  Given  apparent decrease  the  concern  i n t h e RE  r a i s e d by  from t h i s  lumines-  grown  contain  of  the  i n Part I I of this  from  P2^2i2i  behavior  the  two  thesis,  s p e c t r o - g r a d e hexane re-chromatographed  t o p r e p a r e 18, a s e c o n d  advantage  o f t h e RE  ( i f any)  of  the  compound I P r / i P r - 2 3 .  crystals  of  the  two  crystals.  In  o b t a i n e d from the non-red-luminescent m o d i f i c a t i o n  had not been p r e v i o u s l y material.  to the should  u n l e s s the i m p u r i t y were o n l y s o l u b l e  the red-luminescent m o d i f i c a t i o n  from the m e l t and from seeded  As  modifications  i f they belonged  possibility  luminescent  differential  of  the  of  method  dimorphs  i n t h e P2^2i2i b u t n o t i n crystals  Pbca  any  originating  I t c o u l d be e x p e c t e d t h a t b o t h m o d i f i c a t i o n s  same i m p u r i t y  four  o f t h e i n s t r u m e n t , and  the p o s s i b i l i t y took  to  involvement of anthracene,  same b a t c h o n l y d i s p l a y e d t h e RE  modification. the  We  up  This,  no e v i d e n c e o f c o n t a i n i n g  the p o s s i b l e  order to eliminate  or another impurity.  luminescent mentioned  in  97).  intensity.  w h i c h h a d b e e n u s e d as a s t a r t i n g m a t e r i a l devised  by  When t h e  f l u o r e s c e n c e w i t h i n the d e t e c t i o n l i m i t s  d i s p l a y e d no  tions  singlet  b e h a v i o r a s i d e from the accompanying anthracene f l u o r e s c e n c e .  and a l l o t h e r  was  lowest  solutions  l u m i n e s c e n t was  in  order  to  (Pbca) by  manner  this  (P2^2i2^) w e r e  (see P a r t I I ) . this  test  crystallizaMaterial  converted  that into  -245-  350  400  450  500  550  w  (wavelength  Figure Impurity  97. F l u o r e s c e n c e E x c i t a t i o n  i n Crystals  In the remainder impurity  suspect  of this  number  s e c t i o n we r e v i e w t h e p o s s i b l e  one,  e v e n t s known f o r a n t h r a c e n e fluorescence  wavelengths  anthracene,  of  the  clearly  of an excimer  emission,  observed  our  and  of this  RE phenomenon.  unimolecular  phosphorescence  occur  at  glasses,  from  our  1 6 2  N o t o n l y do t h e very  experiments  on t h e o t h e r hand, c o u l d p o s s i b l y Single-photon  excimer  a n d a number o f i t s d e r i v a t i v e s 1 6 4  and i n s o l u t i o n .  e m i s s i o n (Amax 5 5 0 - 5 7 0 nm)  1 6 5  The  photophysical  at  seems t o b e a m u l t i p h o t o n i c p r o c e s s . The  observations.  i n anthracene  hydrocarbon  primary  the  involvement of  different  (-400 a n d 700 nm r e s p e c t i v e l y ) , b u t t h e RE, a s i n d i c a t e d  wavelengths,  of  in  c a n be d i s c a r d e d i m m e d i a t e l y .  the r e q u i r e d a c c u m u l a t i o n t i m e , and  part  (a) and E m i s s i o n (b) o f Anthracene  o f D i e s t e r Me/Me-18.  a s s i g n m e n t o f t h e RE t o a n y  anthracene  nm)  from  different involvement  account  emission  has  in crystals,  1 6 3  for been in  Although the s p e c t r a l region  i s substantially different  from t h a t o f  -246-  the  RE  observed  include  here,  b i p h o t o n i c processes, a r e d anthracene excimer  observed. sandwich  These  1 6 6  occur  emission  when a n t h r a c e n e monomers a r e f o r m e d  ht/(254 nm) > hi/(365  A A  i na  be  fixed  below:  Formation o f Anthracene  from i t s Dimer  Formation o f Anthracene  Sandwich  nm)  2. A A  > (A A)*  (A A)*  >  4. (A A)*  that  can  i n t e r m o l e c u l a r c o n f i g u r a t i o n as s c h e m a t i z e d and e x p l a i n e d  1. A-A  3.  i t i s known t h a t u n d e r s p e c i a l c o n d i t i o n s  —--->  Excimer  A-A  Re-dimerization  A A• + hu  R e d E x c i m e r e m i s s i o n (Amax 570 nm)  F i g u r e 98. F o r m a t i o n  of  Anthracene  Sandwich  Pairs  and  their  Red  Excimer Emission.  In  the  first  s t e p ( e q . 1, F i g u r e 9 8 ) , two a n t h r a c e n e m o l e c u l e s i n a  sandwich c o n f i g u r a t i o n anthracene  dimer  When t h e g r o u n d  (A-A)  (A  A)  are  generated  photochemically  from  i n crystals  of the l a t t e r  ( f i r s t p h o t o n , 254 nm).  s t a t e sandwich dimer  i s irradiated  (second photon,  365  ),  i t c a n r e a c t p h o t o c h e m i c a l l y a t h i g h t e m p e r a t u r e s (200 K) t o g i v e  the  anthracene dimer  characteristic into  be  ( e q . 3) o r , a t l o w e r  r e d luminescence  the r e d . Both  demonstrated  the  to  the arise  the excimeric species  temperatures,  i t can  nm back  emit  a  ( e q . 4, Amax 570 nm) t h a t e x t e n d s b r o a d l y  chemical  reaction  and  the  r e d emission  were  f r o m t h e same i n t e r m e d i a t e w h i c h was p o s t u l a t e d t o (A A ) * .  1  6  6  This excimer emission,  however,  i s  -247-  different that  from  spectral  crystalline possibility The our  the  RE  o b s e r v e d h e r e , a n d , a l t h o u g h i t c o u l d be  differences  environments,  would  require  the  original  a p p r o p r i a t e , f o r immediate t o o c c u r ( e q . 1', should  anthracene but  not  would  3' a n d 4,'  A  intermolecular  (vide  different  emission  molecules i n  Figure 99).  sandwich  this  infra). could to  be  explain i n close  microcrystallites  configuration  should  r e d excimer emission, but s u i t a b l e  photochemically  with a "perfect" monomers  the  r e d excimer e m i s s i o n has n o t been observed i n c r y s t a l s  a n t h r a c e n e ) . The  1')  f o r by  o t h e r arguments c a n a l s o be f o u n d a g a i n s t  i n c r y s t a l s o f d i e s t e r 18  anthracene  (eqs.  accounted  mechanism by w h i c h an a n t h r a c e n e excimer  proximity  they  be  o c c u r r i n g i n c r y s t a l s o f d i e s t e r 18  results  tion  could  argued  (the  o f pure not  be  f o r dimeriza-  Once t h e a n t h r a c e n e d i m e r s a r e f o r m e d ,  r e v e r t back  configuration  t h e be i n a d i s p o s i t i o n  t o two monomers, b u t t h i s (eq.  2').  The  newly  time, formed  favorable f o r r e d excimer emission  Figure 99).  hu A  >  A-A  Dimer F o r m a t i o n  hv 2') A-A  >  A A  Sandwich  (A A)*  Excimer  Pair  Formation  hu 3') A A  4')  --->  (A A)*  > A A + hu  Formation  Red E x c i m e r E m i s s i o n  F i g u r e 99. H y p o t h e t i c a l F o r m a t i o n o f A n t h r a c e n e Red in Crystals of Diester  18.  Excimer  Emission  -248-  Although  the  above model c o u l d e x p l a i n :  c e n c e a t 70 K ( t h e r e the  i s likely  induction period  t o be t h e r m a l  (accumulation  pair  would  argument a g a i n s t red-emitting  probably  b a r r i e r t o d i m e r i z a t i o n ) , (2)  o f the sandwich p a i r would occur a f t e r  some i r r a d i a t i o n t i m e ) , a n d ( 3 ) t h e d e c a y (sandwich  (1) the l a c k o f r e d lumines-  tend  of  the  to diffuse  t h i s m o d e l comes f r o m  the  1 6 6  and i s v e r y  processes,  subsequent  strongly  apart), a very  important  spectrum  of  that  the  anthracene  the  excimer monomer  d i f f e r e n t f r o m t h a t o f X. s u c h a s t h e one d i s c u s s e d  the p a r t i c i p a t i o n o f i m p u r i t y molecules, the  species  s p e c i e s X. The e x c i t a t i o n s p e c t r u m o f t h e a n t h r a c e n e  Although other  RE,  emitting  excitation  m e n t i o n e d above i s a l m o s t i n d i s t i n g u i s h a b l e from absorption,  red  thermal  above t h a t  involve  could e x p l a i n the o r i g i n of the <  behavior  of the species  i t s o r i g i n may b e d i r e c t l y  X seems t o i n d i c a t e  traced  to  the  question  we  tried  dibenzobarrelene  diesters.  What i s t h e RE  In  order  information question. As  Species?  to  answer  the  o n t h i s phenomenon  above by  What i s t h e f a t e o f t h e RE  indicated  in  Figure  96,  asking  ourselves  back t o i t s precursor  gate the p o s s i b i l i t y  the  red-emitting  The  emission  species,  alternatively,  o r s t a r t i n g m a t e r i a l . We d e c i d e d  that X might transform  l u m i n e s c e n t p r o d u c t Y.  closely  related  species?  u l t i m a t e l y decay i n t o a s t a b l e photoproduct, o r revert  a  t o o b t a i n more  S u c h was i n d e e d  into  a  different,  X,  could  i t  could  to investihopefully  f o u n d t o be t h e c a s e .  s p e c t r a o f "pure" samples i n which t h e X s p e c i e s had been  -249-  previously  accumulated  t a k e n out o f the low sec.  The  after  temperature  e m i s s i o n was  each  warming  detecting  w e r e a n a l y z e d a t 77K  r e c o r d e d upon e x c i t a t i o n period  a t 360  d e c a y o f X was  nm was  i n order  and  •  540  3 1 3 , 337 a n d 3 6 0 nm the probability of  accompanying  t h e decay  band w i t h  observed  t h a t the  and increase  Amax a t 510  and  of  X.  thermal  o f a new,  a shoulders a t  '  450  I  500  l  550  l  600  ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ m m  650  700 (wavelength  F i g u r e 100. of  were  nm ( F i g u r e 1 0 0 ) .  •  400  they  t o increase  t h e appearance  somewhat s t r u c t u r e d l u m i n e s c e n c e -475  band  at  r e v e a l i n g when i t was  accompanied by  and a f t e r  a c c e s s o r y f o r p e r i o d s o f a p p r o x i m a t e l y 30  a n y new l u m i n e s c e n c e  Excitation  before  T h e r m a l Decay o f t h e R e d - E m i t t i n g S p e c i e s X and  New S p e c i e s Y.  750 nm)  Appearance  -250-  of  The  new  b a n d , o f a s p e c i e s now  an  allowed  transition  c e n c e mode o f t h e in  Figure  two  m a x i m a a t 430  The  lack  101  along w i t h the 455  nm  The  l u m i n e s c e n c e , as m o s t o f o u r  turned  out  until  there  corresponding although  Interestingly,  to have a l i m i t e d was  no  followed  ance o f the  by  any  the  nm  samples has  irradiations  and  giving  was  was  detectable  fluores-  found to  the had  possess  t o 480  nm.  d e t e c t i o n of i t s been performed  the  to  decay  l u m i n e s c e n c e , and in  also  been  left  l a t t e r band  the  final  section  at  thermally  sample had  decay o f the  discussed  shown  r i s e to t h i s band  found  after  m i n u t e s . The  been  i n the  spectrum of t h i s band,  prevented  species  lifetime  already  characteristics  detected  emission,  had  trace of i t s existence  other  the  i t e x t e n d s f r o m n e a r 380  analytical  a t a m b i e n t t e m p e r a t u r e f o r a few not  excitation  o f a b s o r p t i o n o f Y a t 337  t h i s wavelength.  a l s o had  s i n c e i t c o u l d o n l y be  instrument.  and  c a l l e d Y,  I  was  appearof  this  thesis.  H t-l  z w  H Z  T  350  600  400  650 (wavelength  Figure Species  Y.  101.  Luminescence E x c i t a t i o n  (a) and  Emission  700 nm)  (b) S p e c t r a  of  -251-  A c o r r e l a t i o n b e t w e e n t h e RE a n d t h e p h o t o c h e m i c a l be  reactivity  q u i t e p o s s i b l e a c c o r d i n g t o t h e above o b s e r v a t i o n s . B o t h  cence  phenomena  and  the  at  occurred  state,  the  solid  the  same  time.  Every  time  formation of photoproducts  low  temperatures  two  processes If,  as  diester  RE  at  (different)  barriers  for  of  our  phenomena the  observations  originate  first  from  question  seem light  that  to  indicate,  absorbed  should  by  the  be answered c o n c e r n s  the  of  o f t h e s i n g l e t e x c i t e d s t a t e was  F i g u r e 96, t h e i n v o l v e m e n t no p r o d u c t s the s o l i d  from t h e i r far  for  traenes + 2n  o t h e r t h a n 52 c o u l d b e d e t e c t e d , e i t h e r  state,  this  equation  1  indicated.  in  i t i s known t h a t some d i b e n z o b a r r e l e n e s  singlet manifold.  RE a n d of  transformations take p l a c e . I n  in  those  molecules  e x c i t e d s t a t e from which these  or  either.  to occur.  18,  Although  reaction  Irradiation  the  a n d t h e RE c a n b e p r e v e n t e d  i n d i c a t i n g the existence o f k i n e t i c  many  subsequent  lumines-  the  t h e RE h a d a l s o b e e n p r e s e n t .  u n d e r c o n d i t i o n s t h a t c a u s e no r e a c t i o n d i d n o t g e n e r a t e The  the  di-w-methane r e a r r a n g e m e n t a r e p h o t o c h e m i c a l l y  i n i t i a t e d and take p l a c e in  seems t o  solution can react  The o n l y s i n g l e t s t a t e r e a c t i o n r e p o r t e d s o  6 6  c l a s s o f compounds i s t h e f o r m a t i o n o f d i b e n z o c y c l o o c t a t e -  (86, F i g u r e 102). T h i s r e a c t i o n has been p o s t u l a t e d t o occur by  a d d i t i o n o f the v i n y l i c  double  produce an i n t e r m e d i a t e , 86-1,  bond t o a n e i g h b o r i n g a r o m a t i c  which  has  never  been  detected.  2n  ring to 6 6  This  i n t e r m e d i a t e h a s b e e n p o s t u l a t e d t o t r a n s f o r m t h e r m a l l y b y a r e t r o 2TT + 2TT + 2ir c y c l o a d d i t i o n t o intermediate,  86-1,  form  the  product  d o e s n o t seem t o a c c o u n t  a l t e r n a t i v e s may b e c o n s i d e r e d . conversion  final  8 6 - 1 t o 86 o c c u r s  86.  Although  a  f o r our observations,  single other  F o r i n s t a n c e , i t c a n be p r o p o s e d t h a t t h e  s t e p w i s e . One p o s s i b i l i t y w o u l d b e a 4TT +  2n  retroaddition intermediate this  that  would  (86-11)  give  before  a  benzocyclobutane-orthoquinodimethane  formation  system i s increased w i t h respect  spectroscopic  properties  may  o f 86.  Although  t o t h a t o f 86-1,  not j u s t i f y our  the  102.  lowest  X  and  s i n g l e t State R e a c t i v i t y of  e n e r g y chromophore and  b a n d a r o u n d 370 both  The  Y  cannot discount  (up  t o 580  the p o s s i b i l i t y  ^  very and  t h a t X and  nm  Y may  the  Dibenzobarrelenes.  f a r from the  475  of  observations.  i s e x p e c t e d t o be  i s known t o h a v e t h e  nm,l°^ w h i c h i s s t i l l absorb  1 6  conjugation  i t appears t h a t i t s  experimental  Ortho-quinodimethane, which i s a s i n g l e t s p e c i e s ,  Figure  the  lowest region  absorption in  which  r e s p e c t i v e l y ) . Although originate  from  this  we or  -253-  another  singlet  diesters in  that  the s o l i d  of  the  be  different would  display  simultaneous  Probably  the  of a luminescent by  its  case to  alternative  luminescent  we  of  of the s i n g l e t triplet  18  observed It occur is  luminescence  along  interesting  intermediates,  singlet  the t r i p l e t  i t  state state  additional should  The  We  that  interesting  or from  may  Y from  alternative.  ignore  the  intermediates  have  found  and  a  that  detect  BR-2  illus-  a  triplet  Similar  reaction  probability  to  the  available that i s of  any  of j u s t i f y i n g  the  rearrangement. have  evidence  t h e r e d - e m i t t i n g s p e c i e s X and  a s s i g n e d t o t h e s p e c i e s BR-1  18  compounds.  analyze the p r o b a b i l i t y  t h a t two  t h a t we  of  remembered t h a t  f o r m a t i o n o f X and  will  VI the  products  be  technique  t h e r e a c t i o n pathway o f t h e di-jr-methane to note  reactivity  phenomena ( s e e P a r t  the  i n terms o f the di-7r-methane  recalled  state  s t a t e o f d i b e n z o b a r r e l e n e compounds, and  r e a c t i o n and w i l l  s h o u l d be  c o u l d be  singlet  s t a t e , . t h e r e i s a p p a r e n t l y o n l y one  excited  dibenzobarrelene  have to c o n s i d e r i s the p o s s i b i l i t y  i s a very  the di-7r-methane rearrangement. triplet  that  to exclude unambiguously  d e t e c t any  presence,  e q u a t i o n 2 i n F i g u r e 96.  reaction  other  way  spectroscopy i s a very sensitive  next  the  sizeable  o r i g i n from  cannot  possible  v e r y m i n u t e amounts o f h i g h l y  state  only  its  s o u r c e . A l t h o u g h we  luminescence  t r a t e d by  and  observed  i n t e r m e d i a t e from  demonstrating  indicate  The  have  s t a t e do n o t p r e s e n t t h e l u m i n e s c e n c e  thesis).  involvement would  s t a t e r e a c t i o n , we  been  proposed  rearrangement. for  two  4 6  It  transient  i t s t h e r m a l p r o d u c t Y, s h o w n i n F i g u r e 103  to  which  below.  -254-  -hv(fluor) 18  . . . hv _ . ^ ! l 8 *  "•*••• Jl^  I ISC T  Phos**"*>  -hv(RE)  A  BR-1  BR-l*^--^--  3  18*  -hv(500nm) BR-2*  Figure for  103.  h  - -  v  BR-2  -•  52  D i - r r - M e t h a n e R e a r r a n g e m e n t as  a Possible  the  Luminescence of C r y s t a l l i n e Dibenzobarrelene  The  mechanism by  tively  explain  according  w h i c h the  the  to the  1) A p h o t o n its  The  ---  photochemical  observed  luminescence  a b o v e f i g u r e as  (A < 340  nm)  Diesters.  reactivity results  could  qualita-  be  described  can  follows:  i s a b s o r b e d by  singlet excited state,  Explanation  d i e s t e r 18  in  order  to  form  ^18*.  2)  ^18*  can  revert  to the  3)  ^18*  can  intersystem  ground s t a t e by  fluorescence  (Amax 412  nm),  or,  state, 4)  3  to convert  into  its  triplet  excited  18*. ^16*  can  phosphorescence 5)  cross  ^16*  can  revert  to  its  (Amax 550  nm),  or,  react  ground  photochemically  to  state  give  at  the  low  temperatures  first,  probably  by  a  triplet 6)  s t a t e , d i - 7 r - m e t h a n e b i r a d i c a l BR-1. BR-1  can  now  react  di-jr-methane b i r a d i c a l ,  at  8)  The  temperatures  to  give  the second  BR-2, a n d ,  7) BR-1 c a n a b s o r b a p h o t o n state biradical  high  ( 3 3 5 nm > A >  590)  to  form  an  excited  BR-1*.  e x c i t e d BR-1* c a n decay  i n a r a d i a t i v e manner t o g i v e  the red  l u m i n e s c e n c e o b s e r v e d ( Amax 660 nm). 9) when BR-2 i s f o r m e d , di-7r-methane  final  10) state  i t can e i t h e r  react  thermally  to  form  p h o t o p r o d u c t 52, o r  BR-2 c a n a b s o r b a p h o t o n  (480 nm > A > 370 nm) t o f o r m a n e x c i t e d  BR-2*.  11) BR-2*, i n t u r n , c a n r e v e r t b a c k means o f a r a d i a t i v e  It  should  decay,  be  decay pathway  noted  that  to  i t s ground  state  (BR-2)  other  alternatives,  a r e p o s s i b l e f o r each o f the l u m i n e s c e n t  ground  state dibenzobarrelene  reactant  demonstrated p r e v i o u s l y by Zimmerman The rigid  event  where  a  reaction  ( u s u a l l y g l a s s y ) media i s a  matrix  isolation.  crystalline  including  G.  1 6 9  s u c h as r a d i a t i o n l e s s  intermediates  4 6  i s also and A d a m .  intermediate common  possible  postulated  Closs,  has 1 7 0  also  been  A. H u t c h i s o n  i s formed  analytical  demonstrated 1 7 1  proposed  biradicals  have  discrete  has  been  and detected i n  strategy  by  existences  known  and r a d i c a l several  a n d more r e c e n t l y M.  However, i t s h o u l d be p o i n t e d o u t t h a t o u r o b s e r v a t i o n s the  as  tothe  1 6 8  The s p e c t r o s c o p i c s t u d y o f r a d i c a l s  media  by  (450 > A > 700).  b e t w e e n d i e s t e r 18 a n d i t s p h o t o p r o d u c t 5 2 . D e c a y o f t h e b i r a d i c a l s  in  the  as  pairs  authors  McBride.  a r e unique  1 7 2  i n that  and r e l a t i v e l y  long  lifetimes studies  e v e n a t a m b i e n t t e m p e r a t u r e s . I n c o n t r a s t , i t seems on  reactive  intermediates  up  t o now  have  that  most  been performed a t  t e m p e r a t u r e s a r o u n d 77 K o r b e l o w .  The  I d e n t i t y o f Species  Direct observation  X a n d Y.  o f the  biradicals  involved  i n t h e di-rr-methane  r e a r r a n g e m e n t o f t h e n a p h t h o b a r r e l e n e 73 ( F i g u r e 67 o n p a g e 162 a n d F i g u r e 104  below) hasbeen r e p o r t e d  m a t r i x b y K. S h a f f n e r 353  glassy  EPA  (ether-isopentane-ethanol)  e t a l . ^ F l a s h p h o t o l y t i c a n a l y s i s o f compound 73 a t 1  nm i n t h e t e m p e r a t u r e r a n g e 88-200K r e s u l t e d i n t h e d e t e c t i o n  transient absorption (triplet-triplet K  ina  i n the flash  disappeared.  shown t o c o r r e s p o n d  absorption,  Amax 380 a n d 4 3 0 ) .  photolytic  experiment,  A t t e m p e r a t u r e s above  nsec  i n benzene,  I t was shown t h a t t h e s p e c i e s  isopropanol  Shaffner  readily 380  biradical  e t a l . ^ found f u r t h e r and c o n v i n c i n g evidence f o r t h e i r 1  formation  of the transformation for  210  and g l y c e r o l  t o the t r i p l e t  a s s i g n m e n t f r o m ESR s p e c t r o s c o p i c m e a s u r e m e n t s t h a t w e r e stepwise  73*  responsible f o rthis transient  c o u l d n o t b e a n e x c i t e d s t a t e a n d i t was a s s i g n e d  the  o f ^73*  the spectrum  3  o f t h e new t r a n s i e n t s p e c i e s was r e m a r k a b l y s h o r t a t t h i s  t e m p e r a t u r e , w i t h r = 20+4  BR-B.  excited state  I n i t s p l a c e , a new s h a r p t r a n s i e n t b a n d grew i n a t Amax  nm. T h e l i f e t i m e  triacetate.  t o the t r i p l e t  of a  o f two d i f f e r e n t  triplet  73—>BR-A--->BR-B—>PR0D  consistent  biradicals. could also  with  The p r o g r e s s be  f r o m i n f r a r e d m e a s u r e m e n t s . When t h e t w o l a t t e r a n a l y t i c a l  accounted techniques  w e r e a p p l i e d i t c o u l d b e o b s e r v e d t h a t i r r a d i a t i o n a t 77 K g a v e ESR a n d I R  COPh  Figure  104.  The  Intermediates  in  Di-7r-methane  the  Reaction  of  N a p h t h o b a r r e l e n e 73.  transient least  bands  two h o u r s .  further  corresponding  t o BR-A  When t h e s a m p l e s w e r e warmed  irradiation,  the  corresponding  r e p l a c e d b y t h e s i g n a l s o f a new lasted  without  re-cooled minutes  decrease  in  at  various  94K.  It  ESR  i t s intensity  without  and IR s i g n a l s were  for  The s e c o n d two  of  f o l l o w e d by phosphorescence  photochemical and  shorter lifetime  of only a  few first  Interestingly,  transformation  fluorescence  slowly  h o u r s w h e n i t was  BR-B) was a n i r r e v e r s i b l e p r o c e s s . the  any  intermediate  was a l s o shown t h a t t h e t r a n s f o r m a t i o n o f t h e  (BR-A — > steps  f r o m 77 t o 94K  t r a n s i e n t , BR-B.  t o 77 K, b u t h a d a s i g n i f i c a n t l y  intermediate the  that p e r s i s t e d i n the dark f o r a t  spectroscopy.  c o u l d a l s o be 7 1  The  most  -258-  striking  observation  related  to  t h a t w h i l e compound 73 p r e s e n t e d second  behavior,  t h e ESR the  substantial  the  fact  BR-2  concluded  Shaffner  here,  with  X and  Y,  may  observations  solution  a t the  belong  emissive  o n l y the  By  spectroscopic  second b i r a d i c a l ,  r i g i d i t y . T h e  temperatures  activation  energies  by  (Ea).  of  the  W i t h i n the  T h i s was  intermediate  may  arise  have nanosecond  s o l i d matrix  intermediates  et a l . also mostly  recorded  to c a l c u l a t e  range s t u d i e d (166-200  at  lifetimes  depended  were  i n order  from  difficulty  However, S c h a f f n e r  of the  73  intermediates  out w i t h o u t  that probably  f l a s h spectroscopy  obtained p a r a l l e l e d  of temperature.  carried  compound  two  to the b i r a d i c a l  same t e m p e r a t u r e s .  lifetimes  different  of  above. A p o s s i b l e c o n c e r n  demonstrated t h a t the s t a b i l i z i n g r o l e  values  emission  the p h o t o c h e m i s t r y  c o u l d be  a m b i e n t t e m p e r a t u r e s on b i r a d i c a l s  on  the  the  fact  fluorescence.  to the p o s s i b i l i t y t h a t the  shown i n F i g u r e 103  t h a t our  in fluid  triplet-triplet  t h a t i t was  e t a l . on  credibility  species observed and  intensities  phosphorescence,  the  emissive.  r e p o r t s by  BR-1  signal  authors  t h a t was The  add  a strong  b i r a d i c a l intermediate presented  correlating  BR-B,  t h e e m i s s i o n m e a s u r e m e n t s was  K),  at  their  the  Ea  t h e c h a n g e s i n s o l v e n t v i s c o s i t y as a f u n c t i o n  shown t o be  true for  three  different  solvents  studied. It  seems p o s s i b l e t h a t t h e v i s c o s i t y a n d  t e m p e r a t u r e may  be  glassy  around  matrix  proposed b i r a d i c a l s justified. supports  c o m p a r a b l e t o the v i s c o s i t y and  in  200  K.  the  assignments  of  of a c r y s t a l at  rigidity  I f t h i s were the c a s e , crystalline  It is interesting our  rigidity  medium  of  X  and  can  Y  solvent  the s t a b i l i t y probably  to note that i n d i r e c t s p e c t r a l species  a  as  the  room  of  be  evidence  the well also  biradicals  -259-  i n t e r m e d i a t e s BR-1 It  has  and  BR-2.  been suggested  by J.C.  Scaiano  that biradicals  g e n e r a l l y show 173  t h e same U V - s p e c t r a l c h a r a c t e r i s t i c s manner,  the  biradical ketyl  spectrum  of  from v a l e r p h e n o n e ,  radical  transitions  ketyl  and  fragment  small effect  lying moiety  on  the  those  very closely  i n the  be  105.  The  the spectrum  are  this  of  II the  Clearly,  centered  in  its  w i t h the a l k y l 7 - r a d i c a l c e n t e r has similar  l o c a l i z e d on  ring  the  ( F i g u r e 105)  t o the c a r b o x y l a t e e s t e r group.  Two  In  N o r r i s h type  logic,  two  i d e n t i f i e d i n t h e s p e c i e s BR-1.  o f the m i g r a t i n g aromatic  Figure  1,4-biradical  Using  s h o u l d p r o b a b l y be  center that i s next  resembles  '  by p h o t o r e d u c t i o n o f a c e t o p h e n o n e .  interaction  can  monoradicals.  photochemically generated  transitions.  chromophores  transition  1 7 4  generated  1 7 5  the lowest l y i n g  radical  the  as a n a l o g o u s  R a d i c a l Centers  of  BR-1.  a  different The  lowest  spirocyclooctadienyl and  not  i n the  radical  -260-  The a b s o r p t i o n a n d f l u o r e s c e n c e radical  87-R  spectra f o r  1 0 6 . S a m p l e s  radical  containing d i - t e r t - b u t y l peroxide  87 w e r e i r r a d i a t e d a t 347.1 nm.  consistent  with  A  with studies  shown  in  transient  absorption  Figure  spectrum,  the presence of p r e v i o u s l y known^^ c y c l o h e x a d i e n y l - l i k e  o b s e r v e d . The s p e c t r u m , c o l l e c t e d o n l y  the  r a n g e , was  in  the  vicinity  The l o c a t i o n o f t h i s maximum, s o f a r i n t o t h e  red,  common  for  on e x p e r i m e n t a l  shown  aliphatic  r a d i c a l s b u t has been j u s t i f i e d  grounds.1^7 s t u d i e s  that  these  species  ultraviolet  (Amax 330 nm),  absorption  o f X.  on  also  other have  the u n s u b s t i t u t e d c y c l o h e x a d i e n y l  and  supports  be p o i n t e d emission to  those  from  87-R  in  the  similar  substantially  of  BR-1,  arise  radicals.  from s i g n i f i c a n t  (Amax  87-R was  The  and have  i n the  -360  nm)  reported ^ 1  0  t o t h e one r e p o r t e d f o r  f r o m X a n d 87-R  simple  (-30-50 nm)  cyclohexadienyl  there  observed  i s evident It  should  ( f l u o r e s c e n c e e x c i t a t i o n ) and  red shifted  with  radicals.  respect Although  from the a d d i t i o n a l s u b s t i t u t i o n i s r e a l l y n o t enough  a v a i l a b l e as t o t h e e f f e c t o f s u b s t i t u e n t s on cyclohexadienyl  very  systems  t h a t X may be i d e n t i f i e d w i t h BR-1.  and o t h e r  not  radical.  p o s s i b l y be j u s t i f i e d  case  strong  from the r a d i c a l  o u t , however, t h a t the a b s o r p t i o n  of X are s t i l l  is  strong absorption  the  between the s p e c t r a l data  the hypothesis  t h i s d i f f e r e n c e may present  very  i n agreement w i t h  The f l u o r e s c e n c e  resemblance  cyclohexadienyl  a  t o h a v e a n o r i g i n a t 558 nm w h i c h was v e r y  The  of  c h a r a c t e r i z e d b y a weak a b s o r p t i o n maximum a r o u n d  560 nm.  theoretical  on  and the s p i r o c y c l o o c t a -  r a d i c a l s , was visible  spirocyclooctadienyl  have been d e t e r m i n e d r e c e n t l y i n c o n n e c t i o n  the neophyl rearrangement o f the 2-phenylethyl  diene  the  the  spectral  information features  spectral differences could  i n t e r a c t i o n b e t w e e n t h e two r a d i c a l  centers,  of also  which  -261-  we have i g n o r e d  to this  point.  (a)  •  i  1  450  500  550  i  600  nm Figure Radical  106. (a) The Neophyl Rearrangement o f the S p i r o c y c l o o c t a d i e n y l  87-R, and, (b) A b s o r p t i o n  Turning have  our a t t e n t i o n t o the second luminescent s p e c i e s  tentatively  assigned  can be a p p r e c i a t e d expected  from  spectroscopic number  of  Spectrum o f 87-R.  Y,  which  we  as the second di-?r-methane b i r a d i c a l BR-2, i t  t h a t the lowest e l e c t r o n i c t r a n s i t i o n s can p r o b a b l y  the  benzylic-localized  r a d i c a l center  be  ( F i g u r e 107). The  p r o p e r t i e s o f b e n z y l i c r a d i c a l s have a l s o been s t u d i e d by  workers  found t h a t b e n z y l u l t r a v i o l e t region  and  are  r e l a t i v e l y well documented.  r a d i c a l s e x h i b i t a strong absorption  band  178  a  I t has been in  the  near  (Amax 305 and 318) , and a v e r y weak and s t r u c t u r e d band  -262-  in the v i s i b l e and  r e g i o n ( 3 6 0 - 4 6 0 nm) w i t h t w o r e l a t i v e l y  450 nm. ^ 1  8  to  have  f r o m t h e p r o p o s e d s p e c i e s BR-2,  two m a x i m a i n t h e v i s i b l e  ( 4 3 0 a n d 4 6 0 nm r e s p e c t i v e l y ) .  the  r a d i c a l a l s o compares r e m a r k a b l y  s p e c i e s Y. P r e s e n t i n g v i b r a t i o n a l the  benzyl  radical  covers  The  the  fluorescence  consisting